diff --git a/spring-web/src/main/java/org/springframework/http/HttpHeaders.java b/spring-web/src/main/java/org/springframework/http/HttpHeaders.java
index 7ce36aad2e..0c428ff240 100644
--- a/spring-web/src/main/java/org/springframework/http/HttpHeaders.java
+++ b/spring-web/src/main/java/org/springframework/http/HttpHeaders.java
@@ -1063,11 +1063,9 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	/**
 	 * Set the (new) entity tag of the body, as specified by the {@code ETag} header.
 	 */
-	public void setETag(@Nullable String eTag) {
-		if (eTag != null) {
-			Assert.isTrue(eTag.startsWith("\"") || eTag.startsWith("W/\""), "ETag does not start with W/\" or \"");
-			Assert.isTrue(eTag.endsWith("\""), "ETag does not end with \"");
-			set(ETAG, eTag);
+	public void setETag(@Nullable String tag) {
+		if (tag != null) {
+			set(ETAG, ETag.quoteETagIfNecessary(tag));
 		}
 		else {
 			remove(ETAG);
diff --git a/spring-web/src/main/java/org/springframework/http/ResponseEntity.java b/spring-web/src/main/java/org/springframework/http/ResponseEntity.java
index ea62bc565a..2a55dfcbb7 100644
--- a/spring-web/src/main/java/org/springframework/http/ResponseEntity.java
+++ b/spring-web/src/main/java/org/springframework/http/ResponseEntity.java
@@ -568,9 +568,8 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 		}
 
 		@Override
-		public BodyBuilder eTag(@Nullable String eTag) {
-			eTag = (eTag != null ? ETag.quoteETagIfNecessary(eTag) : eTag);
-			this.headers.setETag(eTag);
+		public BodyBuilder eTag(@Nullable String tag) {
+			this.headers.setETag(tag);
 			return this;
 		}
 
diff --git a/spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java b/spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java
index 09c833ce47..49f64e6223 100644
--- a/spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java
+++ b/spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java
@@ -417,13 +417,13 @@ public class DefaultServerWebExchange implements ServerWebExchange {
 		addCachingResponseHeaders(eTag, lastModified);
 	}
 
-	private void addCachingResponseHeaders(@Nullable String eTag, Instant lastModified) {
+	private void addCachingResponseHeaders(@Nullable String tag, Instant lastModified) {
 		if (SAFE_METHODS.contains(getRequest().getMethod())) {
 			if (lastModified.isAfter(Instant.EPOCH) && getResponseHeaders().getLastModified() == -1) {
 				getResponseHeaders().setLastModified(lastModified.toEpochMilli());
 			}
-			if (StringUtils.hasLength(eTag) && getResponseHeaders().getETag() == null) {
-				getResponseHeaders().setETag(ETag.quoteETagIfNecessary(eTag));
+			if (StringUtils.hasLength(tag) && getResponseHeaders().getETag() == null) {
+				getResponseHeaders().setETag(tag);
 			}
 		}
 	}
diff --git a/spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java b/spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java
index c0057254bc..7767b4ea41 100644
--- a/spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java
+++ b/spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java
@@ -214,15 +214,15 @@ class HttpHeadersTests {
 	}
 
 	@Test
-	void illegalETagWithoutQuotes() {
-		String eTag = "v2.6";
-		assertThatIllegalArgumentException().isThrownBy(() -> headers.setETag(eTag));
+	void eTagWithoutQuotes() {
+		headers.setETag("v2.6");
+		assertThat(headers.getETag()).isEqualTo("\"v2.6\"");
 	}
 
 	@Test
-	void illegalWeakETagWithoutLeadingQuote() {
-		String etag = "W/v2.6\"";
-		assertThatIllegalArgumentException().isThrownBy(() -> headers.setETag(etag));
+	void weakETagWithoutLeadingQuote() {
+		headers.setETag("W/v2.6\"");
+		assertThat(headers.getETag()).isEqualTo("\"W/v2.6\"\"");
 	}
 
 	@Test
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultEntityResponseBuilder.java b/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultEntityResponseBuilder.java
index 75c0126085..d31d0ff8a9 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultEntityResponseBuilder.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultEntityResponseBuilder.java
@@ -148,9 +148,8 @@ class DefaultEntityResponseBuilder<T> implements EntityResponse.Builder<T> {
 	}
 
 	@Override
-	public EntityResponse.Builder<T> eTag(String eTag) {
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public EntityResponse.Builder<T> eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}
 
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerResponseBuilder.java b/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerResponseBuilder.java
index 00443c9d48..1b2f372b7c 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerResponseBuilder.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerResponseBuilder.java
@@ -147,10 +147,8 @@ class DefaultServerResponseBuilder implements ServerResponse.BodyBuilder {
 	}
 
 	@Override
-	public ServerResponse.BodyBuilder eTag(String eTag) {
-		Assert.notNull(eTag, "etag must not be null");
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public ServerResponse.BodyBuilder eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}
 
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.java b/spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.java
index 674d6d2567..941308e137 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -332,8 +332,7 @@ public class VersionResourceResolver extends AbstractResourceResolver {
 
 		@Override
 		public HttpHeaders getResponseHeaders() {
-			HttpHeaders headers = (this.original instanceof HttpResource httpResource ?
-					httpResource.getResponseHeaders() : new HttpHeaders());
+			HttpHeaders headers = (this.original instanceof HttpResource hr ? hr.getResponseHeaders() : new HttpHeaders());
 			headers.setETag("W/\"" + this.version + "\"");
 			return headers;
 		}
diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultEntityResponseBuilder.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultEntityResponseBuilder.java
index bed228e264..d4947e0746 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultEntityResponseBuilder.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultEntityResponseBuilder.java
@@ -166,9 +166,8 @@ final class DefaultEntityResponseBuilder<T> implements EntityResponse.Builder<T>
 	}
 
 	@Override
-	public EntityResponse.Builder<T> eTag(String eTag) {
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public EntityResponse.Builder<T> eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}
 
diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerResponseBuilder.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerResponseBuilder.java
index 46ea10a80f..a6117d4caf 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerResponseBuilder.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerResponseBuilder.java
@@ -127,10 +127,8 @@ class DefaultServerResponseBuilder implements ServerResponse.BodyBuilder {
 	}
 
 	@Override
-	public ServerResponse.BodyBuilder eTag(String eTag) {
-		Assert.notNull(eTag, "etag must not be null");
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public ServerResponse.BodyBuilder eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}