diff --git a/spring-test/src/main/java/org/springframework/test/context/ContextCustomizer.java b/spring-test/src/main/java/org/springframework/test/context/ContextCustomizer.java
index d9462faadb..a190bb3a34 100644
--- a/spring-test/src/main/java/org/springframework/test/context/ContextCustomizer.java
+++ b/spring-test/src/main/java/org/springframework/test/context/ContextCustomizer.java
@@ -35,6 +35,7 @@ import org.springframework.context.ConfigurableApplicationContext;
  * @see ContextCustomizerFactory
  * @see org.springframework.test.context.support.AbstractContextLoader#customizeContext
  */
+@FunctionalInterface
 public interface ContextCustomizer {
 
 	/**
diff --git a/spring-test/src/main/java/org/springframework/test/context/ContextCustomizerFactory.java b/spring-test/src/main/java/org/springframework/test/context/ContextCustomizerFactory.java
index 9f07700a38..3f8113a6f1 100644
--- a/spring-test/src/main/java/org/springframework/test/context/ContextCustomizerFactory.java
+++ b/spring-test/src/main/java/org/springframework/test/context/ContextCustomizerFactory.java
@@ -34,6 +34,7 @@ import java.util.List;
  * @author Sam Brannen
  * @since 4.3
  */
+@FunctionalInterface
 public interface ContextCustomizerFactory {
 
 	/**