diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java
index e627122ac31..59218e86792 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java
@@ -250,14 +250,14 @@ class ReactiveWebServerFactoryAutoConfigurationTests {
 	@Test
 	void forwardedHeaderTransformerShouldBeConfigured() {
 		this.contextRunner.withUserConfiguration(HttpHandlerConfiguration.class)
-				.withPropertyValues("server.forward-headers-strategy=framework")
+				.withPropertyValues("server.forward-headers-strategy=framework", "server.port=0")
 				.run((context) -> assertThat(context).hasSingleBean(ForwardedHeaderTransformer.class));
 	}
 
 	@Test
 	void forwardedHeaderTransformerWhenStrategyNotFilterShouldNotBeConfigured() {
 		this.contextRunner.withUserConfiguration(HttpHandlerConfiguration.class)
-				.withPropertyValues("server.forward-headers-strategy=native")
+				.withPropertyValues("server.forward-headers-strategy=native", "server.port=0")
 				.run((context) -> assertThat(context).doesNotHaveBean(ForwardedHeaderTransformer.class));
 	}
 
@@ -265,7 +265,7 @@ class ReactiveWebServerFactoryAutoConfigurationTests {
 	void forwardedHeaderTransformerWhenAlreadyRegisteredShouldBackOff() {
 		this.contextRunner
 				.withUserConfiguration(ForwardedHeaderTransformerConfiguration.class, HttpHandlerConfiguration.class)
-				.withPropertyValues("server.forward-headers-strategy=framework")
+				.withPropertyValues("server.forward-headers-strategy=framework", "server.port=0")
 				.run((context) -> assertThat(context).hasSingleBean(ForwardedHeaderTransformer.class));
 	}
 
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java
index 6096fd86fe7..700698c5e4b 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java
@@ -155,7 +155,8 @@ class ServletWebServerFactoryAutoConfigurationTests {
 				AnnotationConfigServletWebServerApplicationContext::new)
 						.withClassLoader(new FilteredClassLoader(Tomcat.class, HttpServer.class))
 						.withConfiguration(AutoConfigurations.of(ServletWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(JettyServerCustomizerConfiguration.class);
+						.withUserConfiguration(JettyServerCustomizerConfiguration.class)
+						.withPropertyValues("server.port:0");
 		runner.run((context) -> {
 			JettyServletWebServerFactory factory = context.getBean(JettyServletWebServerFactory.class);
 			assertThat(factory.getServerCustomizers()).hasSize(1);
@@ -168,7 +169,8 @@ class ServletWebServerFactoryAutoConfigurationTests {
 				AnnotationConfigServletWebServerApplicationContext::new)
 						.withClassLoader(new FilteredClassLoader(Tomcat.class, HttpServer.class, Server.class))
 						.withConfiguration(AutoConfigurations.of(ServletWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(UndertowDeploymentInfoCustomizerConfiguration.class);
+						.withUserConfiguration(UndertowDeploymentInfoCustomizerConfiguration.class)
+						.withPropertyValues("server.port:0");
 		runner.run((context) -> {
 			UndertowServletWebServerFactory factory = context.getBean(UndertowServletWebServerFactory.class);
 			assertThat(factory.getDeploymentInfoCustomizers()).hasSize(1);
@@ -181,7 +183,8 @@ class ServletWebServerFactoryAutoConfigurationTests {
 				AnnotationConfigServletWebServerApplicationContext::new)
 						.withClassLoader(new FilteredClassLoader(Tomcat.class, HttpServer.class, Server.class))
 						.withConfiguration(AutoConfigurations.of(ServletWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(UndertowBuilderCustomizerConfiguration.class);
+						.withUserConfiguration(UndertowBuilderCustomizerConfiguration.class)
+						.withPropertyValues("server.port:0");
 		runner.run((context) -> {
 			UndertowServletWebServerFactory factory = context.getBean(UndertowServletWebServerFactory.class);
 			assertThat(factory.getBuilderCustomizers()).hasSize(1);