diff --git a/spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java b/spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java
index dff4c9ced0..093f9f9667 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -331,7 +331,7 @@ public class MessageHeaderAccessor {
 	protected void verifyType(@Nullable String headerName, @Nullable Object headerValue) {
 		if (headerName != null && headerValue != null) {
 			if (MessageHeaders.ERROR_CHANNEL.equals(headerName) ||
-					MessageHeaders.REPLY_CHANNEL.endsWith(headerName)) {
+					MessageHeaders.REPLY_CHANNEL.equals(headerName)) {
 				if (!(headerValue instanceof MessageChannel || headerValue instanceof String)) {
 					throw new IllegalArgumentException(
 							"'" + headerName + "' header value must be a MessageChannel or String");
diff --git a/spring-messaging/src/test/java/org/springframework/messaging/support/MessageBuilderTests.java b/spring-messaging/src/test/java/org/springframework/messaging/support/MessageBuilderTests.java
index 42aae2a371..cc4078c35b 100644
--- a/spring-messaging/src/test/java/org/springframework/messaging/support/MessageBuilderTests.java
+++ b/spring-messaging/src/test/java/org/springframework/messaging/support/MessageBuilderTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -34,6 +34,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 /**
  * @author Mark Fisher
  * @author Rossen Stoyanchev
+ * @author Mengqi Xu
  */
 class MessageBuilderTests {
 
@@ -238,4 +239,22 @@ class MessageBuilderTests {
 		assertThat(message3.getHeaders().get("foo")).isEqualTo("bar3");
 	}
 
+	@Test  // gh-34949
+	void buildMessageWithReplyChannelHeader() {
+		MessageHeaderAccessor headerAccessor = new MessageHeaderAccessor();
+		MessageBuilder<?> messageBuilder = MessageBuilder.withPayload("payload").setHeaders(headerAccessor);
+
+		headerAccessor.setHeader(MessageHeaders.REPLY_CHANNEL, "foo");
+		Message<?> message1 = messageBuilder.build();
+		assertThat(message1.getHeaders().get(MessageHeaders.REPLY_CHANNEL)).isEqualTo("foo");
+
+		headerAccessor.setHeader("hannel", 0);
+		Message<?> message2 = messageBuilder.build();
+		assertThat(message2.getHeaders().get("hannel")).isEqualTo(0);
+
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> headerAccessor.setHeader(MessageHeaders.REPLY_CHANNEL, 0))
+				.withMessage("'%s' header value must be a MessageChannel or String", MessageHeaders.REPLY_CHANNEL);
+	}
+
 }