diff --git a/spring-web/src/main/java/org/springframework/http/converter/multipart/PartGenerator.java b/spring-web/src/main/java/org/springframework/http/converter/multipart/PartGenerator.java
index 5e1046e13ae..34693f64071 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/multipart/PartGenerator.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/multipart/PartGenerator.java
@@ -293,7 +293,7 @@ final class PartGenerator implements MultipartParser.PartListener {
 
 		private void switchToFile(DataBuffer current, boolean last) {
 			FileState fileState = new FileState(this.headers, PartGenerator.this.fileStorageDirectory);
-			this.content.forEach(fileState::writeBuffer);
+			this.content.forEach(buffer -> fileState.onBody(buffer, false));
 			fileState.onBody(current, last);
 			PartGenerator.this.state = fileState;
 		}
diff --git a/spring-web/src/test/java/org/springframework/http/converter/multipart/MultipartHttpMessageConverterTests.java b/spring-web/src/test/java/org/springframework/http/converter/multipart/MultipartHttpMessageConverterTests.java
index 14200fd12ae..edffedf97c4 100644
--- a/spring-web/src/test/java/org/springframework/http/converter/multipart/MultipartHttpMessageConverterTests.java
+++ b/spring-web/src/test/java/org/springframework/http/converter/multipart/MultipartHttpMessageConverterTests.java
@@ -236,6 +236,17 @@ class MultipartHttpMessageConverterTests {
 					.isInstanceOf(HttpMessageConversionException.class).hasMessage("Part exceeded the disk usage limit of 35 bytes");
 		}
 
+		@Test // gh-37238
+		void readMultipartMaxDiskUsageExceededAcrossBufferedPrefix() throws Exception {
+			MockHttpInputMessage response = createMultipartResponse("large-file.multipart", "B");
+			converter.setMaxInMemorySize(1935);
+			// just over the max in memory, will only fail if buffered memory is counted for when writing to file
+			converter.setMaxDiskUsagePerPart(1945);
+			assertThatThrownBy(() -> converter.read(ResolvableType.forClassWithGenerics(MultiValueMap.class, String.class, Part.class), response, null))
+					.isInstanceOf(HttpMessageConversionException.class)
+					.hasMessage("Part exceeded the disk usage limit of 1945 bytes");
+		}
+
 		@Test
 		void readMultipartUnnamedPart() throws Exception {
 			MockHttpInputMessage response = createMultipartResponse("simple.multipart", "simple-boundary");
diff --git a/spring-web/src/test/resources/org/springframework/http/multipart/large-file.multipart b/spring-web/src/test/resources/org/springframework/http/multipart/large-file.multipart
new file mode 100644
index 00000000000..deb03115c67
--- /dev/null
+++ b/spring-web/src/test/resources/org/springframework/http/multipart/large-file.multipart
@@ -0,0 +1,6 @@
+--B
+Content-Disposition: form-data; name="file"; filename="test.txt"
+Content-Type: application/octet-stream
+
+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+--B--