diff --git a/clients/src/main/java/org/apache/kafka/clients/producer/Callback.java b/clients/src/main/java/org/apache/kafka/clients/producer/Callback.java
index 2eb7ebc882b..5c8f159ac82 100644
--- a/clients/src/main/java/org/apache/kafka/clients/producer/Callback.java
+++ b/clients/src/main/java/org/apache/kafka/clients/producer/Callback.java
@@ -20,6 +20,7 @@ package org.apache.kafka.clients.producer;
  * A callback interface that the user can implement to allow code to execute when the request is complete. This callback
  * will generally execute in the background I/O thread so it should be fast.
  */
+@FunctionalInterface
 public interface Callback {
 
     /**
diff --git a/connect/runtime/src/main/java/org/apache/kafka/connect/util/Callback.java b/connect/runtime/src/main/java/org/apache/kafka/connect/util/Callback.java
index fd62fc172f4..f628e822274 100644
--- a/connect/runtime/src/main/java/org/apache/kafka/connect/util/Callback.java
+++ b/connect/runtime/src/main/java/org/apache/kafka/connect/util/Callback.java
@@ -19,6 +19,7 @@ package org.apache.kafka.connect.util;
 /**
  * Generic interface for callbacks
  */
+@FunctionalInterface
 public interface Callback<V> {
     /**
      * Invoked upon completion of the operation.