diff --git a/spring-core/src/test/java/org/springframework/core/codec/ByteArrayDecoderTests.java b/spring-core/src/test/java/org/springframework/core/codec/ByteArrayDecoderTests.java
index b350958ba9f..c138f84f9b5 100644
--- a/spring-core/src/test/java/org/springframework/core/codec/ByteArrayDecoderTests.java
+++ b/spring-core/src/test/java/org/springframework/core/codec/ByteArrayDecoderTests.java
@@ -69,7 +69,7 @@ public class ByteArrayDecoderTests extends AbstractDataBufferAllocatingTestCase
 	public void decodeError() {
 		DataBuffer fooBuffer = stringBuffer("foo");
 		Flux<DataBuffer> source =
-				Flux.just(fooBuffer).mergeWith(Flux.error(new RuntimeException()));
+				Flux.just(fooBuffer).concatWith(Flux.error(new RuntimeException()));
 		Flux<byte[]> output = this.decoder.decode(source,
 				ResolvableType.forClassWithGenerics(Publisher.class, byte[].class),
 				null, Collections.emptyMap());
diff --git a/spring-core/src/test/java/org/springframework/core/codec/ByteBufferDecoderTests.java b/spring-core/src/test/java/org/springframework/core/codec/ByteBufferDecoderTests.java
index a40de1a44ad..16db16ee16a 100644
--- a/spring-core/src/test/java/org/springframework/core/codec/ByteBufferDecoderTests.java
+++ b/spring-core/src/test/java/org/springframework/core/codec/ByteBufferDecoderTests.java
@@ -68,7 +68,7 @@ public class ByteBufferDecoderTests extends AbstractDataBufferAllocatingTestCase
 	public void decodeError() {
 		DataBuffer fooBuffer = stringBuffer("foo");
 		Flux<DataBuffer> source =
-				Flux.just(fooBuffer).mergeWith(Flux.error(new RuntimeException()));
+				Flux.just(fooBuffer).concatWith(Flux.error(new RuntimeException()));
 		Flux<ByteBuffer> output = this.decoder.decode(source,
 				ResolvableType.forClassWithGenerics(Publisher.class, ByteBuffer.class),
 				null, Collections.emptyMap());
diff --git a/spring-core/src/test/java/org/springframework/core/codec/ResourceDecoderTests.java b/spring-core/src/test/java/org/springframework/core/codec/ResourceDecoderTests.java
index 2b79e2a767f..d5dacf9270f 100644
--- a/spring-core/src/test/java/org/springframework/core/codec/ResourceDecoderTests.java
+++ b/spring-core/src/test/java/org/springframework/core/codec/ResourceDecoderTests.java
@@ -77,7 +77,7 @@ public class ResourceDecoderTests extends AbstractDataBufferAllocatingTestCase {
 	public void decodeError() {
 		DataBuffer fooBuffer = stringBuffer("foo");
 		Flux<DataBuffer> source =
-				Flux.just(fooBuffer).mergeWith(Flux.error(new RuntimeException()));
+				Flux.just(fooBuffer).concatWith(Flux.error(new RuntimeException()));
 
 
 		Flux<Resource> result = this.decoder
diff --git a/spring-core/src/test/java/org/springframework/core/codec/StringDecoderTests.java b/spring-core/src/test/java/org/springframework/core/codec/StringDecoderTests.java
index f40bf243422..5cb549acf82 100644
--- a/spring-core/src/test/java/org/springframework/core/codec/StringDecoderTests.java
+++ b/spring-core/src/test/java/org/springframework/core/codec/StringDecoderTests.java
@@ -177,7 +177,7 @@ public class StringDecoderTests extends AbstractDataBufferAllocatingTestCase {
 	public void decodeError() {
 		DataBuffer fooBuffer = stringBuffer("foo\n");
 		Flux<DataBuffer> source =
-				Flux.just(fooBuffer).mergeWith(Flux.error(new RuntimeException()));
+				Flux.just(fooBuffer).concatWith(Flux.error(new RuntimeException()));
 
 		Flux<String> output = this.decoder.decode(source,
 				ResolvableType.forClass(String.class), null, Collections.emptyMap());
diff --git a/spring-web/src/test/java/org/springframework/http/codec/FormHttpMessageReaderTests.java b/spring-web/src/test/java/org/springframework/http/codec/FormHttpMessageReaderTests.java
index 8b2f151532d..cefd2e36f2f 100644
--- a/spring-web/src/test/java/org/springframework/http/codec/FormHttpMessageReaderTests.java
+++ b/spring-web/src/test/java/org/springframework/http/codec/FormHttpMessageReaderTests.java
@@ -106,7 +106,7 @@ public class FormHttpMessageReaderTests extends AbstractDataBufferAllocatingTest
 	public void readFormError() {
 		DataBuffer fooBuffer = stringBuffer("name=value");
 		Flux<DataBuffer> body =
-				Flux.just(fooBuffer).mergeWith(Flux.error(new RuntimeException()));
+				Flux.just(fooBuffer).concatWith(Flux.error(new RuntimeException()));
 		MockServerHttpRequest request = request(body);
 
 		Flux<MultiValueMap<String, String>> result = this.reader.read(null, request, null);
diff --git a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java
index f8a6d902b79..5b50fab7d17 100644
--- a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java
+++ b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java
@@ -176,7 +176,7 @@ public class ServerSentEventHttpMessageReaderTests extends AbstractDataBufferAll
 
 		Flux<DataBuffer> body =
 				Flux.just(stringBuffer("data:foo\ndata:bar\n\ndata:baz\n\n"))
-						.mergeWith(Flux.error(new RuntimeException()));
+						.concatWith(Flux.error(new RuntimeException()));
 
 		MockServerHttpRequest request = MockServerHttpRequest.post("/")
 				.body(body);