diff --git a/spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java b/spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java
index f07065be85f8..e98856167fa8 100644
--- a/spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java
+++ b/spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java
@@ -157,7 +157,7 @@ protected UriComponentsBuilder(UriComponentsBuilder other) {
 		this.port = other.port;
 		this.pathBuilder = other.pathBuilder.cloneBuilder();
 		this.uriVariables.putAll(other.uriVariables);
-		this.queryParams.putAll(other.queryParams);
+		this.queryParams.addAll(other.queryParams);
 		this.fragment = other.fragment;
 		this.encodeTemplate = other.encodeTemplate;
 		this.charset = other.charset;
diff --git a/spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java b/spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java
index d19c2740a29c..7fe6bfa1fbc3 100644
--- a/spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java
+++ b/spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java
@@ -918,30 +918,32 @@ void parsesEmptyUri() {
 		assertThat(components.toString()).isEqualTo("");
 	}
 
-	@Test
+	@Test  // gh-25243
 	void testCloneAndMerge() {
 		UriComponentsBuilder builder1 = UriComponentsBuilder.newInstance();
-		builder1.scheme("http").host("e1.com").path("/p1").pathSegment("ps1").queryParam("q1").fragment("f1").encode();
+		builder1.scheme("http").host("e1.com").path("/p1").pathSegment("ps1").queryParam("q1", "x").fragment("f1").encode();
 
-		UriComponentsBuilder builder2 = (UriComponentsBuilder) builder1.clone();
+		UriComponentsBuilder builder2 = builder1.cloneBuilder();
 		builder2.scheme("https").host("e2.com").path("p2").pathSegment("{ps2}").queryParam("q2").fragment("f2");
 
+		builder1.queryParam("q1", "y");  // one more entry for an existing parameter
+
 		UriComponents result1 = builder1.build();
 		assertThat(result1.getScheme()).isEqualTo("http");
 		assertThat(result1.getHost()).isEqualTo("e1.com");
 		assertThat(result1.getPath()).isEqualTo("/p1/ps1");
-		assertThat(result1.getQuery()).isEqualTo("q1");
+		assertThat(result1.getQuery()).isEqualTo("q1=x&q1=y");
 		assertThat(result1.getFragment()).isEqualTo("f1");
 
 		UriComponents result2 = builder2.buildAndExpand("ps2;a");
 		assertThat(result2.getScheme()).isEqualTo("https");
 		assertThat(result2.getHost()).isEqualTo("e2.com");
 		assertThat(result2.getPath()).isEqualTo("/p1/ps1/p2/ps2%3Ba");
-		assertThat(result2.getQuery()).isEqualTo("q1&q2");
+		assertThat(result2.getQuery()).isEqualTo("q1=x&q2");
 		assertThat(result2.getFragment()).isEqualTo("f2");
 	}
 
-	@Test // gh-24772
+	@Test  // gh-24772
 	void testDeepClone() {
 		HashMap<String, Object> vars = new HashMap<>();
 		vars.put("ps1", "foo");
@@ -951,7 +953,7 @@ void testDeepClone() {
 		builder1.scheme("http").host("e1.com").userInfo("user:pwd").path("/p1").pathSegment("{ps1}")
 				.pathSegment("{ps2}").queryParam("q1").fragment("f1").uriVariables(vars).encode();
 
-		UriComponentsBuilder builder2 = (UriComponentsBuilder) builder1.clone();
+		UriComponentsBuilder builder2 = builder1.cloneBuilder();
 
 		UriComponents result1 = builder1.build();
 		assertThat(result1.getScheme()).isEqualTo("http");