diff --git a/spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/ReactiveReturnTypeTests.java b/spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/ReactiveReturnTypeTests.java
index 5d310bb3f6e..f4b4d0564f9 100644
--- a/spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/ReactiveReturnTypeTests.java
+++ b/spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/ReactiveReturnTypeTests.java
@@ -52,7 +52,7 @@ class ReactiveReturnTypeTests {
 				.andReturn();
 
 		mockMvc.perform(asyncDispatch(mvcResult))
-				.andExpect(content().string("data:event0\n\ndata:event1\n\ndata:event2\n\n"));
+				.andExpect(content().string("data: event0\n\ndata: event1\n\ndata: event2\n\n"));
 	}
 
 
diff --git a/spring-web/src/main/java/org/springframework/http/codec/ServerSentEvent.java b/spring-web/src/main/java/org/springframework/http/codec/ServerSentEvent.java
index e77f3b8a08b..87ea1c62133 100644
--- a/spring-web/src/main/java/org/springframework/http/codec/ServerSentEvent.java
+++ b/spring-web/src/main/java/org/springframework/http/codec/ServerSentEvent.java
@@ -96,7 +96,7 @@ public final class ServerSentEvent<T> {
 
 	/**
 	 * Return a StringBuilder with the id, event, retry, and comment fields fully
-	 * serialized, and also appending "data:" if there is data.
+	 * serialized, and also appending "data: " if there is data.
 	 * @since 6.2.1
 	 */
 	public String format() {
@@ -116,7 +116,7 @@ public final class ServerSentEvent<T> {
 			sb.append('\n');
 		}
 		if (this.data != null) {
-			sb.append("data:");
+			sb.append("data: ");
 		}
 		return sb.toString();
 	}
diff --git a/spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java b/spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java
index 274780fda31..b1f2b19e957 100644
--- a/spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java
+++ b/spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java
@@ -69,7 +69,7 @@ public class Jackson2JsonEncoder extends AbstractJackson2Encoder {
 
 	private static PrettyPrinter initSsePrettyPrinter() {
 		DefaultPrettyPrinter printer = new DefaultPrettyPrinter();
-		printer.indentObjectsWith(new DefaultIndenter("  ", "\ndata:"));
+		printer.indentObjectsWith(new DefaultIndenter("  ", "\ndata: "));
 		return printer;
 	}
 
diff --git a/spring-web/src/main/java/org/springframework/http/codec/json/JacksonJsonEncoder.java b/spring-web/src/main/java/org/springframework/http/codec/json/JacksonJsonEncoder.java
index 9caf6aba742..9ac9a989d2e 100644
--- a/spring-web/src/main/java/org/springframework/http/codec/json/JacksonJsonEncoder.java
+++ b/spring-web/src/main/java/org/springframework/http/codec/json/JacksonJsonEncoder.java
@@ -117,7 +117,7 @@ public class JacksonJsonEncoder extends AbstractJacksonEncoder<JsonMapper> {
 
 	private static PrettyPrinter initSsePrettyPrinter() {
 		DefaultPrettyPrinter printer = new DefaultPrettyPrinter();
-		printer.indentObjectsWith(new DefaultIndenter("  ", "\ndata:"));
+		printer.indentObjectsWith(new DefaultIndenter("  ", "\ndata: "));
 		return printer;
 	}
 
diff --git a/spring-web/src/main/java/org/springframework/http/converter/AbstractJacksonHttpMessageConverter.java b/spring-web/src/main/java/org/springframework/http/converter/AbstractJacksonHttpMessageConverter.java
index b9f730f0dcf..2005351bcee 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/AbstractJacksonHttpMessageConverter.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/AbstractJacksonHttpMessageConverter.java
@@ -175,7 +175,7 @@ public abstract class AbstractJacksonHttpMessageConverter<T extends ObjectMapper
 
 	private PrettyPrinter initSsePrettyPrinter() {
 		DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
-		prettyPrinter.indentObjectsWith(new DefaultIndenter("  ", "\ndata:"));
+		prettyPrinter.indentObjectsWith(new DefaultIndenter("  ", "\ndata: "));
 		return prettyPrinter;
 	}
 
diff --git a/spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java b/spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java
index 6f545772293..fb480e132a6 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java
@@ -108,7 +108,7 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 	protected AbstractJackson2HttpMessageConverter(ObjectMapper objectMapper) {
 		this.defaultObjectMapper = objectMapper;
 		DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
-		prettyPrinter.indentObjectsWith(new DefaultIndenter("  ", "\ndata:"));
+		prettyPrinter.indentObjectsWith(new DefaultIndenter("  ", "\ndata: "));
 		this.ssePrettyPrinter = prettyPrinter;
 	}
 
diff --git a/spring-web/src/main/java/org/springframework/web/util/SseUtils.java b/spring-web/src/main/java/org/springframework/web/util/SseUtils.java
index ceead086ab7..f20fe345d71 100644
--- a/spring-web/src/main/java/org/springframework/web/util/SseUtils.java
+++ b/spring-web/src/main/java/org/springframework/web/util/SseUtils.java
@@ -31,9 +31,9 @@ public abstract class SseUtils {
 	/**
 	 * Append {@code value} to {@code output}, replacing each line separator
 	 * ({@code "\n"}, {@code "\r"}, or {@code "\r\n"}) it contains with a new
-	 * {@code field} line (that is, {@code "\n" + field + ":"}). This keeps a
-	 * multi-line field value from breaking out of the current SSE field when
-	 * written on the wire.
+	 * {@code field} line (that is, {@code "\n" + field + ": "}, or
+	 * {@code "\n:"} for a comment). This keeps a multi-line field value from
+	 * breaking out of the current SSE field when written on the wire.
 	 * @param field the name of the SSE field that {@code value} belongs to
 	 * (for example, {@code "data"}), or an empty string for a comment
 	 * @param value the field value to escape and append
@@ -44,7 +44,7 @@ public abstract class SseUtils {
 			output.append(value);
 			return;
 		}
-		String lineSeparatorReplacement = "\n" + field + ":";
+		String lineSeparatorReplacement = "\n" + field + (field.isEmpty() ? ":" : ": ");
 		int length = value.length();
 		for (int i = 0; i < length; i++) {
 			char c = value.charAt(i);
diff --git a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageWriterTests.java b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageWriterTests.java
index 705a2d3af29..0025e1cc4ee 100644
--- a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageWriterTests.java
+++ b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageWriterTests.java
@@ -85,7 +85,7 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 
 		StepVerifier.create(outputMessage.getBody())
 				.consumeNextWith(stringConsumer(
-						"id:c42\nevent:foo\nretry:123\n:bla\n:bla bla\n:bla bla bla\ndata:bar\n\n"))
+						"id:c42\nevent:foo\nretry:123\n:bla\n:bla bla\n:bla bla bla\ndata: bar\n\n"))
 				.expectComplete()
 				.verify();
 	}
@@ -99,8 +99,8 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 		testWrite(source, outputMessage, String.class);
 
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:foo\n\n"))
-				.consumeNextWith(stringConsumer("data:bar\n\n"))
+				.consumeNextWith(stringConsumer("data: foo\n\n"))
+				.consumeNextWith(stringConsumer("data: bar\n\n"))
 				.expectComplete()
 				.verify();
 	}
@@ -114,9 +114,9 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 		testWrite(source, outputMessage, String.class);
 
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:first\ndata:second\n\n"))
-				.consumeNextWith(stringConsumer("data:first\ndata:second\n\n"))
-				.consumeNextWith(stringConsumer("data:first\ndata:second\n\n"))
+				.consumeNextWith(stringConsumer("data: first\ndata: second\n\n"))
+				.consumeNextWith(stringConsumer("data: first\ndata: second\n\n"))
+				.consumeNextWith(stringConsumer("data: first\ndata: second\n\n"))
 				.expectComplete()
 				.verify();
 	}
@@ -136,7 +136,7 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 				.consumeNextWith(dataBuffer -> {
 					String value = dataBuffer.toString(charset);
 					DataBufferUtils.release(dataBuffer);
-					assertThat(value).isEqualTo("data:\u00A3\n\n");
+					assertThat(value).isEqualTo("data: \u00A3\n\n");
 				})
 				.expectComplete()
 				.verify();
@@ -151,10 +151,10 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 		testWrite(source, outputMessage, Pojo.class);
 
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("data: "))
 				.consumeNextWith(stringConsumer("{\"foo\":\"foofoo\",\"bar\":\"barbar\"}"))
 				.consumeNextWith(stringConsumer("\n\n"))
-				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("data: "))
 				.consumeNextWith(stringConsumer("{\"foo\":\"foofoofoo\",\"bar\":\"barbarbar\"}"))
 				.consumeNextWith(stringConsumer("\n\n"))
 				.expectComplete()
@@ -173,19 +173,19 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 		testWrite(source, outputMessage, Pojo.class);
 
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("data: "))
 				.consumeNextWith(stringConsumer("""
 						{
-						data:  "foo" : "foofoo",
-						data:  "bar" : "barbar"
-						data:}"""))
+						data:   "foo" : "foofoo",
+						data:   "bar" : "barbar"
+						data: }"""))
 				.consumeNextWith(stringConsumer("\n\n"))
-				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("data: "))
 				.consumeNextWith(stringConsumer("""
 						{
-						data:  "foo" : "foofoofoo",
-						data:  "bar" : "barbarbar"
-						data:}"""))
+						data:   "foo" : "foofoofoo",
+						data:   "bar" : "barbarbar"
+						data: }"""))
 				.consumeNextWith(stringConsumer("\n\n"))
 				.expectComplete()
 				.verify();
@@ -203,7 +203,7 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 
 		assertThat(outputMessage.getHeaders().getContentType()).isEqualTo(mediaType);
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:", charset))
+				.consumeNextWith(stringConsumer("data: ", charset))
 				.consumeNextWith(stringConsumer("{\"foo\":\"foo\uD834\uDD1E\",\"bar\":\"bar\uD834\uDD1E\"}", charset))
 				.consumeNextWith(stringConsumer("\n\n", charset))
 				.expectComplete()
diff --git a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventTests.java b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventTests.java
index 9e1a1d7c76f..1790523458c 100644
--- a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventTests.java
+++ b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventTests.java
@@ -51,7 +51,7 @@ class ServerSentEventTests {
 	void supportMultiLineComments(String newLine, String description) {
 		ServerSentEvent<String> event = ServerSentEvent.<String>builder()
 				.comment("foo" + newLine + "bar" + newLine + "baz").data("payload").build();
-		assertThat(event.format()).isEqualTo(":foo\n:bar\n:baz\ndata:");
+		assertThat(event.format()).isEqualTo(":foo\n:bar\n:baz\ndata: ");
 	}
 
 	private static Stream<Arguments> newLineCharacters() {
diff --git a/spring-web/src/test/java/org/springframework/http/converter/json/JacksonJsonHttpMessageConverterTests.java b/spring-web/src/test/java/org/springframework/http/converter/json/JacksonJsonHttpMessageConverterTests.java
index 66964c9f140..f19cec8015d 100644
--- a/spring-web/src/test/java/org/springframework/http/converter/json/JacksonJsonHttpMessageConverterTests.java
+++ b/spring-web/src/test/java/org/springframework/http/converter/json/JacksonJsonHttpMessageConverterTests.java
@@ -415,7 +415,7 @@ class JacksonJsonHttpMessageConverterTests {
 				MediaType.APPLICATION_JSON, outputMessage, null);
 		String result = outputMessage.getBodyAsString(StandardCharsets.UTF_8);
 
-		assertThat(result).isEqualTo("{\ndata:  \"name\" : \"Jason\"\ndata:}");
+		assertThat(result).isEqualTo("{\ndata:   \"name\" : \"Jason\"\ndata: }");
 	}
 
 	@Test
diff --git a/spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java b/spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java
index 2d570301278..f9dcda30ed4 100644
--- a/spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java
+++ b/spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java
@@ -385,7 +385,7 @@ class MappingJackson2HttpMessageConverterTests {
 		this.converter.writeInternal(bean, null, outputMessage);
 		String result = outputMessage.getBodyAsString(StandardCharsets.UTF_8);
 
-		assertThat(result).isEqualTo("{\ndata:  \"name\" : \"Jason\"\ndata:}");
+		assertThat(result).isEqualTo("{\ndata:   \"name\" : \"Jason\"\ndata: }");
 	}
 
 	@Test
diff --git a/spring-web/src/test/java/org/springframework/web/util/SseUtilsTests.java b/spring-web/src/test/java/org/springframework/web/util/SseUtilsTests.java
index 94a649a0e2d..77b43781da6 100644
--- a/spring-web/src/test/java/org/springframework/web/util/SseUtilsTests.java
+++ b/spring-web/src/test/java/org/springframework/web/util/SseUtilsTests.java
@@ -44,9 +44,9 @@ class SseUtilsTests {
 	@MethodSource("newLineCharacters")
 	void appendFieldValueReplacesLineSeparatorWithFieldPrefix(String newLine, String description) {
 		StringBuilder sb = new StringBuilder();
-		sb.append("data:");
+		sb.append("data: ");
 		SseUtils.appendFieldValue("data", "first" + newLine + "second", sb);
-		assertThat(sb).hasToString("data:first\ndata:second");
+		assertThat(sb).hasToString("data: first\ndata: second");
 	}
 
 	@ParameterizedTest(name = "{1}")
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java b/spring-webflux/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java
index b0a7c0e41df..c2502081db4 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java
@@ -590,7 +590,7 @@ public class ViewResolutionResultHandler extends HandlerResultHandlerSupport imp
 
 			ServerSentEvent<?> sse = (ServerSentEvent<?>) hints;
 			CharSequence eventText = (sse != null ? sse.format() :
-					(fragment.viewName() != null ? "event:" + fragment.viewName() + "\n" : "") + "data:");
+					(fragment.viewName() != null ? "event:" + fragment.viewName() + "\n" : "") + "data: ");
 
 			DataBuffer prefix = encodeText(eventText.toString(), charset, bufferFactory);
 			DataBuffer suffix = encodeText("\n\n", charset, bufferFactory);
diff --git a/spring-webflux/src/test/java/org/springframework/web/reactive/result/view/FragmentViewResolutionResultHandlerTests.java b/spring-webflux/src/test/java/org/springframework/web/reactive/result/view/FragmentViewResolutionResultHandlerTests.java
index db95230fc13..74deefb5e4a 100644
--- a/spring-webflux/src/test/java/org/springframework/web/reactive/result/view/FragmentViewResolutionResultHandlerTests.java
+++ b/spring-webflux/src/test/java/org/springframework/web/reactive/result/view/FragmentViewResolutionResultHandlerTests.java
@@ -107,14 +107,14 @@ class FragmentViewResolutionResultHandlerTests {
 				on(Handler.class).resolveReturnType(Flux.class, Fragment.class),
 				"""
 				event:fragment1
-				data:<p>
-				data:	Hello Foo
-				data:</p>
+				data: <p>
+				data: 	Hello Foo
+				data: </p>
 
 				event:fragment2
-				data:<p>
-				data:	Hello Bar
-				data:</p>
+				data: <p>
+				data: 	Hello Bar
+				data: </p>
 
 				""");
 	}
@@ -126,10 +126,10 @@ class FragmentViewResolutionResultHandlerTests {
 				on(Handler.class).resolveReturnType(Flux.class, Fragment.class),
 				"""
 				event:fragment1
-				data:<p>
-				data:	Hello Foo
-				data: and Bar
-				data:</p>
+				data: <p>
+				data: 	Hello Foo
+				data:  and Bar
+				data: </p>
 
 				""");
 	}
@@ -147,15 +147,15 @@ class FragmentViewResolutionResultHandlerTests {
 				"""
 				id:id1
 				event:event1
-				data:<p>
-				data:	Hello Foo
-				data:</p>
+				data: <p>
+				data: 	Hello Foo
+				data: </p>
 
 				id:id2
 				event:event2
-				data:<p>
-				data:	Hello Bar
-				data:</p>
+				data: <p>
+				data: 	Hello Bar
+				data: </p>
 
 				""");
 	}
diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/function/SseServerResponse.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/function/SseServerResponse.java
index 52f6b6f6523..8064ebe5ebb 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/function/SseServerResponse.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/function/SseServerResponse.java
@@ -177,6 +177,9 @@ final class SseServerResponse extends AbstractServerResponse {
 
 		private SseBuilder field(String name, String value) {
 			this.builder.append(name).append(':');
+			if (!name.isEmpty()) {
+				this.builder.append(' ');
+			}
 			SseUtils.appendFieldValue(name, value, this.builder);
 			this.builder.append('\n');
 			return this;
@@ -200,7 +203,7 @@ final class SseServerResponse extends AbstractServerResponse {
 
 		@SuppressWarnings("unchecked")
 		private void writeObject(Object data) throws IOException {
-			this.builder.append("data:");
+			this.builder.append("data: ");
 			try {
 				this.outputMessage.getBody().write(builderBytes());
 				Class<?> dataClass = data.getClass();
diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitter.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitter.java
index 42ba09c6855..22b4adf83e8 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitter.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitter.java
@@ -240,7 +240,7 @@ public class SseEmitter extends ResponseBodyEmitter {
 			if (object instanceof ModelAndView mav && !this.hasName && mav.getViewName() != null) {
 				name(mav.getViewName());
 			}
-			append("data:");
+			append("data: ");
 			saveAppendedText(TEXT_PLAIN);
 			if (object instanceof String text) {
 				writeStringData(text, mediaType);
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/function/SseServerResponseTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/function/SseServerResponseTests.java
index b95da1ab4e9..4c08bb652a3 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/function/SseServerResponseTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/function/SseServerResponseTests.java
@@ -71,7 +71,7 @@ class SseServerResponseTests {
 		ModelAndView mav = response.writeTo(this.mockRequest, this.mockResponse, context);
 		assertThat(mav).isNull();
 
-		String expected = "data:" + body + "\n\n";
+		String expected = "data: " + body + "\n\n";
 		assertThat(this.mockResponse.getContentAsString()).isEqualTo(expected);
 	}
 
@@ -127,7 +127,7 @@ class SseServerResponseTests {
 		ModelAndView mav = response.writeTo(this.mockRequest, this.mockResponse, context);
 		assertThat(mav).isNull();
 
-		String expected = "data:{\"name\":\"John Doe\",\"age\":42}\n\n";
+		String expected = "data: {\"name\":\"John Doe\",\"age\":42}\n\n";
 		assertThat(this.mockResponse.getContentAsString()).isEqualTo(expected);
 	}
 
@@ -151,10 +151,10 @@ class SseServerResponseTests {
 		assertThat(mav).isNull();
 
 		String expected = """
-				data:{
-				data:  "name" : "John Doe",
-				data:  "age" : 42
-				data:}
+				data: {
+				data:   "name" : "John Doe",
+				data:   "age" : 42
+				data: }
 
 				""";
 		assertThat(this.mockResponse.getContentAsString()).isEqualTo(expected);
@@ -186,7 +186,7 @@ class SseServerResponseTests {
 				:comment line 1
 				:comment line 2
 				retry:1000
-				data:data
+				data: data
 
 				""";
 		assertThat(this.mockResponse.getContentAsString()).isEqualTo(expected);
@@ -229,7 +229,7 @@ class SseServerResponseTests {
 		ModelAndView mav = response.writeTo(this.mockRequest, this.mockResponse, context);
 		assertThat(mav).isNull();
 
-		String expected = "data:line1\ndata:line2\ndata:line3\n\n";
+		String expected = "data: line1\ndata: line2\ndata: line3\n\n";
 		assertThat(this.mockResponse.getContentAsString()).isEqualTo(expected);
 	}
 
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/FragmentRenderingStreamTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/FragmentRenderingStreamTests.java
index f478dd9dfa9..f34e55fca1a 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/FragmentRenderingStreamTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/FragmentRenderingStreamTests.java
@@ -104,14 +104,14 @@ class FragmentRenderingStreamTests {
 		assertThat(this.response.getContentType()).isEqualTo("text/event-stream");
 		assertThat(this.response.getContentAsString()).isEqualTo(("""
 				event:fragment1
-				data:<p>
-				data:	Hello Foo
-				data:</p>
+				data: <p>
+				data: 	Hello Foo
+				data: </p>
 
 				event:fragment2
-				data:<p>
-				data:	Hello Bar
-				data:</p>
+				data: <p>
+				data: 	Hello Bar
+				data: </p>
 
 				"""));
 	}
@@ -134,14 +134,14 @@ class FragmentRenderingStreamTests {
 		assertThat(this.response.getContentType()).isEqualTo("text/event-stream");
 		assertThat(this.response.getContentAsString()).isEqualTo(("""
 				event:fragment1
-				data:<p>
-				data:	Hello Foo
-				data:</p>
+				data: <p>
+				data: 	Hello Foo
+				data: </p>
 
 				event:fragment2
-				data:<p>
-				data:	Hello Bar
-				data:</p>
+				data: <p>
+				data: 	Hello Bar
+				data: </p>
 
 				"""));
 	}
@@ -163,10 +163,10 @@ class FragmentRenderingStreamTests {
 		assertThat(this.response.getContentType()).isEqualTo("text/event-stream");
 		assertThat(this.response.getContentAsString()).isEqualTo(("""
 				event:fragment1
-				data:<p>
-				data:	Hello Foo
-				data: and Bar
-				data:</p>
+				data: <p>
+				data: 	Hello Foo
+				data:  and Bar
+				data: </p>
 
 				"""));
 	}
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ReactiveTypeHandlerTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ReactiveTypeHandlerTests.java
index 65e4fd2c1f3..32c031f4238 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ReactiveTypeHandlerTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ReactiveTypeHandlerTests.java
@@ -267,7 +267,7 @@ class ReactiveTypeHandlerTests {
 		sink.tryEmitNext("baz");
 		sink.tryEmitComplete();
 
-		assertThat(emitterHandler.getValuesAsText()).isEqualTo("data:foo\n\ndata:bar\n\ndata:baz\n\n");
+		assertThat(emitterHandler.getValuesAsText()).isEqualTo("data: foo\n\ndata: bar\n\ndata: baz\n\n");
 	}
 
 	@Test
@@ -286,7 +286,7 @@ class ReactiveTypeHandlerTests {
 		sink.tryEmitNext(ServerSentEvent.builder("baz").id("3").build());
 		sink.tryEmitComplete();
 
-		assertThat(emitterHandler.getValuesAsText()).isEqualTo("id:1\ndata:foo\n\nid:2\ndata:bar\n\nid:3\ndata:baz\n\n");
+		assertThat(emitterHandler.getValuesAsText()).isEqualTo("id:1\ndata: foo\n\nid:2\ndata: bar\n\nid:3\ndata: baz\n\n");
 	}
 
 	@ParameterizedTest
@@ -453,7 +453,7 @@ class ReactiveTypeHandlerTests {
 
 			sink.tryEmitComplete();
 
-			assertThat(emitterHandler.getValuesAsText()).isEqualTo("data:emitted value\n\n");
+			assertThat(emitterHandler.getValuesAsText()).isEqualTo("data: emitted value\n\n");
 			assertThat(emitterHandler.getSavedRequest()).isSameAs(this.servletRequest);
 		}
 		finally {
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapterTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapterTests.java
index 123168ca25e..9edab27d853 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapterTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapterTests.java
@@ -218,7 +218,7 @@ class RequestMappingHandlerAdapterTests {
 
 		assertThat(this.response.getStatus()).isEqualTo(200);
 		assertThat(this.response.getHeader("Content-Type")).isEqualTo("text/event-stream");
-		assertThat(this.response.getContentAsString()).isEqualTo("data:event 1\n\ndata:event 2\n\n");
+		assertThat(this.response.getContentAsString()).isEqualTo("data: event 1\n\ndata: event 2\n\n");
 	}
 
 	@Test
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandlerTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandlerTests.java
index a4f904aa432..005a0174d71 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandlerTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandlerTests.java
@@ -218,8 +218,8 @@ class ResponseBodyEmitterReturnValueHandlerTests {
 				event:update
 				id:1
 				retry:5000
-				data:{"id":1,"name":"Joe"}
-				data:{"id":2,"name":"John"}
+				data: {"id":1,"name":"Joe"}
+				data: {"id":2,"name":"John"}
 
 				"""));
 	}
@@ -235,7 +235,7 @@ class ResponseBodyEmitterReturnValueHandlerTests {
 		assertThat(this.response.getStatus()).isEqualTo(200);
 
 		assertThat(this.response.getContentType()).isEqualTo("text/event-stream");
-		assertThat(this.response.getContentAsString()).isEqualTo("data:foo\n\ndata:bar\n\ndata:baz\n\n");
+		assertThat(this.response.getContentAsString()).isEqualTo("data: foo\n\ndata: bar\n\ndata: baz\n\n");
 	}
 
 	@Test
@@ -274,7 +274,7 @@ class ResponseBodyEmitterReturnValueHandlerTests {
 		assertThat(this.response.getStatus()).isEqualTo(200);
 
 		assertThat(this.response.getContentType()).isEqualTo("text/event-stream");
-		assertThat(this.response.getContentAsString()).isEqualTo("data:foo123\n\ndata:bar123\n\ndata:baz123\n\n");
+		assertThat(this.response.getContentAsString()).isEqualTo("data: foo123\n\ndata: bar123\n\ndata: baz123\n\n");
 	}
 
 	@Test // gh-21972
@@ -357,7 +357,7 @@ class ResponseBodyEmitterReturnValueHandlerTests {
 		assertThat(this.request.isAsyncStarted()).isTrue();
 		assertThat(this.response.getStatus()).isEqualTo(200);
 		assertThat(this.response.getContentType()).isEqualTo("text/event-stream");
-		assertThat(this.response.getContentAsString()).isEqualTo("data:foo\n\ndata:bar\n\n");
+		assertThat(this.response.getContentAsString()).isEqualTo("data: foo\n\ndata: bar\n\n");
 	}
 
 	@Test // gh-36357
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitterTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitterTests.java
index 2ff5bfebd50..97f7746cbe5 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitterTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitterTests.java
@@ -65,7 +65,7 @@ class SseEmitterTests {
 	void send() throws Exception {
 		this.emitter.send("foo");
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, "data:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, "data: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "foo");
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
@@ -75,7 +75,7 @@ class SseEmitterTests {
 	void sendWithMediaType() throws Exception {
 		this.emitter.send("foo", MediaType.TEXT_PLAIN);
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, "data:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, "data: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "foo", MediaType.TEXT_PLAIN);
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
@@ -92,7 +92,7 @@ class SseEmitterTests {
 	void sendEventWithDataLine() throws Exception {
 		this.emitter.send(event().data("foo"));
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, "data:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, "data: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "foo");
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
@@ -102,9 +102,9 @@ class SseEmitterTests {
 	void sendEventWithTwoDataLines() throws Exception {
 		this.emitter.send(event().data("foo").data("bar"));
 		this.handler.assertSentObjectCount(5);
-		this.handler.assertObject(0, "data:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, "data: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "foo");
-		this.handler.assertObject(2, "\ndata:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(2, "\ndata: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(3, "bar");
 		this.handler.assertObject(4, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
@@ -115,8 +115,8 @@ class SseEmitterTests {
 	void sendEventWithMultiline(String newLineChars, String description) throws Exception {
 		this.emitter.send(event().data("foo" + newLineChars + "bar" + newLineChars + "baz"));
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, "data:", TEXT_PLAIN_UTF8);
-		this.handler.assertObject(1, "foo\ndata:bar\ndata:baz");
+		this.handler.assertObject(0, "data: ", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(1, "foo\ndata: bar\ndata: baz");
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
 	}
@@ -126,8 +126,8 @@ class SseEmitterTests {
 	void sendEventWithMultilineWithMediaType(String newLineChars, String description) throws Exception {
 		this.emitter.send(event().data("foo" + newLineChars + "bar" + newLineChars + "baz", MediaType.TEXT_PLAIN));
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, "data:", TEXT_PLAIN_UTF8);
-		this.handler.assertObject(1, "foo\ndata:bar\ndata:baz", MediaType.TEXT_PLAIN);
+		this.handler.assertObject(0, "data: ", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(1, "foo\ndata: bar\ndata: baz", MediaType.TEXT_PLAIN);
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
 	}
@@ -136,7 +136,7 @@ class SseEmitterTests {
 	void sendEventFull() throws Exception {
 		this.emitter.send(event().comment("blah").name("test").reconnectTime(5000L).id("1").data("foo"));
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, ":blah\nevent:test\nretry:5000\nid:1\ndata:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, ":blah\nevent:test\nretry:5000\nid:1\ndata: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "foo");
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
@@ -146,9 +146,9 @@ class SseEmitterTests {
 	void sendEventFullWithTwoDataLinesInTheMiddle() throws Exception {
 		this.emitter.send(event().comment("blah").data("foo").data("bar").name("test").reconnectTime(5000L).id("1"));
 		this.handler.assertSentObjectCount(5);
-		this.handler.assertObject(0, ":blah\ndata:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, ":blah\ndata: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "foo");
-		this.handler.assertObject(2, "\ndata:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(2, "\ndata: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(3, "bar");
 		this.handler.assertObject(4, "\nevent:test\nretry:5000\nid:1\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);
@@ -173,7 +173,7 @@ class SseEmitterTests {
 	void supportMultiLineComments(String newLineChars, String description) throws Exception {
 		this.emitter.send(event().comment("foo" + newLineChars + "bar" + newLineChars + "baz").data("payload"));
 		this.handler.assertSentObjectCount(3);
-		this.handler.assertObject(0, ":foo\n:bar\n:baz\ndata:", TEXT_PLAIN_UTF8);
+		this.handler.assertObject(0, ":foo\n:bar\n:baz\ndata: ", TEXT_PLAIN_UTF8);
 		this.handler.assertObject(1, "payload");
 		this.handler.assertObject(2, "\n\n", TEXT_PLAIN_UTF8);
 		this.handler.assertWriteCount(1);