diff --git a/spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java b/spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java
index aa091045a86..03aab3dcb6c 100644
--- a/spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java
+++ b/spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java
@@ -118,14 +118,12 @@ public class EncoderHttpMessageWriter<T> implements HttpMessageWriter<T> {
 
 		if (inputStream instanceof Mono) {
 			HttpHeaders headers = message.getHeaders();
-			if (headers.getFirst(HttpHeaders.CONTENT_LENGTH) == null) {
-				return Mono.from(body)
-						.defaultIfEmpty(message.bufferFactory().wrap(new byte[0]))
-						.flatMap(buffer -> {
-							headers.setContentLength(buffer.readableByteCount());
-							return message.writeWith(Mono.just(buffer));
-						});
-			}
+			return Mono.from(body)
+					.defaultIfEmpty(message.bufferFactory().wrap(new byte[0]))
+					.flatMap(buffer -> {
+						headers.setContentLength(buffer.readableByteCount());
+						return message.writeWith(Mono.just(buffer));
+					});
 		}
 
 		return (isStreamingMediaType(contentType) ?
diff --git a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractServerHttpResponse.java b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractServerHttpResponse.java
index ab396dc9209..8be6b1899bd 100644
--- a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractServerHttpResponse.java
+++ b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractServerHttpResponse.java
@@ -45,6 +45,7 @@ import org.springframework.util.MultiValueMap;
  * @author Rossen Stoyanchev
  * @author Juergen Hoeller
  * @author Sebastien Deleuze
+ * @author Brian Clozel
  * @since 5.0
  */
 public abstract class AbstractServerHttpResponse implements ServerHttpResponse {
@@ -174,13 +175,21 @@ public abstract class AbstractServerHttpResponse implements ServerHttpResponse {
 	@Override
 	public final Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
 		return new ChannelSendOperator<>(body,
-				writePublisher -> doCommit(() -> writeWithInternal(writePublisher)));
+				writePublisher -> doCommit(() -> writeWithInternal(writePublisher)))
+				.doOnError(t -> removeContentLength());
 	}
 
 	@Override
 	public final Mono<Void> writeAndFlushWith(Publisher<? extends Publisher<? extends DataBuffer>> body) {
 		return new ChannelSendOperator<>(body,
-				writePublisher -> doCommit(() -> writeAndFlushWithInternal(writePublisher)));
+				writePublisher -> doCommit(() -> writeAndFlushWithInternal(writePublisher)))
+				.doOnError(t -> removeContentLength());
+	}
+
+	private void removeContentLength() {
+		if (!this.isCommitted()) {
+			this.getHeaders().remove(HttpHeaders.CONTENT_LENGTH);
+		}
 	}
 
 	@Override
diff --git a/spring-web/src/test/java/org/springframework/http/server/reactive/ServerHttpResponseTests.java b/spring-web/src/test/java/org/springframework/http/server/reactive/ServerHttpResponseTests.java
index 651e9c55bd8..55746952ca5 100644
--- a/spring-web/src/test/java/org/springframework/http/server/reactive/ServerHttpResponseTests.java
+++ b/spring-web/src/test/java/org/springframework/http/server/reactive/ServerHttpResponseTests.java
@@ -29,6 +29,7 @@ import reactor.core.publisher.Mono;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DefaultDataBuffer;
 import org.springframework.core.io.buffer.DefaultDataBufferFactory;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.ResponseCookie;
 
 import static junit.framework.TestCase.assertTrue;
@@ -75,12 +76,14 @@ public class ServerHttpResponseTests {
 	@Test
 	public void writeWithError() throws Exception {
 		TestServerHttpResponse response = new TestServerHttpResponse();
+		response.getHeaders().setContentLength(12);
 		IllegalStateException error = new IllegalStateException("boo");
 		response.writeWith(Flux.error(error)).onErrorResume(ex -> Mono.empty()).block();
 
 		assertFalse(response.statusCodeWritten);
 		assertFalse(response.headersWritten);
 		assertFalse(response.cookiesWritten);
+		assertFalse(response.getHeaders().containsKey(HttpHeaders.CONTENT_LENGTH));
 		assertTrue(response.body.isEmpty());
 	}