diff --git a/spring-web/src/main/java/org/springframework/web/util/WhatWgUrlParser.java b/spring-web/src/main/java/org/springframework/web/util/WhatWgUrlParser.java
index d2d10298745..6b5c508eb95 100644
--- a/spring-web/src/main/java/org/springframework/web/util/WhatWgUrlParser.java
+++ b/spring-web/src/main/java/org/springframework/web/util/WhatWgUrlParser.java
@@ -55,6 +55,7 @@ import org.springframework.util.Assert;
  * with {@code EXTRA}.
  *
  * @author Arjen Poutsma
+ * @author Sebastien Deleuze
  * @since 6.2
  */
 @SuppressWarnings({"SameParameterValue", "BooleanMethodIsAlwaysInverted"})
@@ -277,31 +278,12 @@ final class WhatWgUrlParser {
 	}
 
 	private static String domainToAscii(String domain, boolean beStrict) {
-		// If beStrict is false, domain is an ASCII string, and strictly splitting domain on U+002E (.)
-		// does not produce any item that starts with an ASCII case-insensitive match for "xn--",
-		// this step is equivalent to ASCII lowercasing domain.
+		// If beStrict is false and domain is an ASCII string, the algorithm returns domain lowercased
+		// regardless of Unicode ToASCII's outcome, due to web compatibility. In particular, the WhatWG
+		// spec deliberately does not reject invalid or ambiguous "xn--" (ACE) labels here. See the note in
+		// https://url.spec.whatwg.org/#concept-domain-to-ascii and web-platform-tests url cases
 		if (!beStrict && containsOnlyAscii(domain)) {
-			int dotIdx = domain.indexOf('.');
-			boolean onlyLowerCase = true;
-			while (dotIdx != -1) {
-				if (domain.length() - dotIdx > 4) {
-					// ASCII case-insensitive match for "xn--"
-					int ch0 = domain.codePointAt(dotIdx + 1);
-					int ch1 = domain.codePointAt(dotIdx + 2);
-					int ch2 = domain.codePointAt(dotIdx + 3);
-					int ch3 = domain.codePointAt(dotIdx + 4);
-					if ((ch0 == 'x' || ch0 == 'X') &&
-							(ch1 == 'n' || ch1 == 'N') &&
-							ch2 == '-' && ch3 == '_') {
-						onlyLowerCase = false;
-						break;
-					}
-				}
-				dotIdx = domain.indexOf('.', dotIdx + 1);
-			}
-			if (onlyLowerCase) {
-				return domain.toLowerCase(Locale.ENGLISH);
-			}
+			return domain.toLowerCase(Locale.ENGLISH);
 		}
 		// Let result be the result of running Unicode ToASCII (https://www.unicode.org/reports/tr46/#ToASCII)
 		// with domain_name set to domain, UseSTD3ASCIIRules set to beStrict, CheckHyphens set to false,
diff --git a/spring-web/src/test/java/org/springframework/web/util/WhatWgUrlParserTests.java b/spring-web/src/test/java/org/springframework/web/util/WhatWgUrlParserTests.java
index c4fadb5f0fa..ad4c4e697a3 100644
--- a/spring-web/src/test/java/org/springframework/web/util/WhatWgUrlParserTests.java
+++ b/spring-web/src/test/java/org/springframework/web/util/WhatWgUrlParserTests.java
@@ -23,6 +23,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 
 /**
  * @author Arjen Poutsma
+ * @author Sebastien Deleuze
  */
 class WhatWgUrlParserTests {
 
@@ -43,6 +44,25 @@ class WhatWgUrlParserTests {
 		testParse("//other.info/parent/../foo/bar", "", "other.info", null, "/foo/bar", null, null);
 	}
 
+	@Test
+	void parseAsciiHost() {
+		// Pure ASCII host is lowercased
+		testParse("https://EXAMPLE.com/foo", "https", "example.com", null, "/foo", null, null);
+		// ASCII "xn--" (ACE) labels are accepted and lowercased (in any case), not validated or rejected.
+		// See https://url.spec.whatwg.org/#concept-domain-to-ascii and web-platform-tests url cases.
+		testParse("https://a.b.c.xn--pokxncvks", "https", "a.b.c.xn--pokxncvks", null, "", null, null);
+		testParse("https://a.b.c.XN--pokxncvks", "https", "a.b.c.xn--pokxncvks", null, "", null, null);
+		testParse("https://a.b.c.Xn--pokxncvks", "https", "a.b.c.xn--pokxncvks", null, "", null, null);
+		// A trailing non-numeric "xn--" label keeps a numeric-looking host as a domain, not an IPv4 address.
+		testParse("https://10.0.0.xn--pokxncvks", "https", "10.0.0.xn--pokxncvks", null, "", null, null);
+		testParse("https://10.0.0.XN--pokxncvks", "https", "10.0.0.xn--pokxncvks", null, "", null, null);
+		testParse("https://10.0.0.xN--pokxncvks", "https", "10.0.0.xn--pokxncvks", null, "", null, null);
+		// Leading ACE label is handled too, and an empty "xn--" label is accepted (not a failure)
+		testParse("https://XN--pokxncvks.example", "https", "xn--pokxncvks.example", null, "", null, null);
+		testParse("https://xn--/", "https", "xn--", null, "/", null, null);
+		testParse("file://xn--/p", "file", "xn--", null, "/p", null, null);
+	}
+
 	private void testParse(String input, String scheme, @Nullable String host, @Nullable String port, String path, @Nullable String query, @Nullable String fragment) {
 		WhatWgUrlParser.UrlRecord result = WhatWgUrlParser.parse(input, EMPTY_URL_RECORD, null, null);
 		assertThat(result.scheme()).as("Invalid scheme").isEqualTo(scheme);