diff --git a/protobuf/src/main/java/io/grpc/protobuf/ProtoUtils.java b/protobuf/src/main/java/io/grpc/protobuf/ProtoUtils.java
index 7d197ab82c..c936b3c1b4 100644
--- a/protobuf/src/main/java/io/grpc/protobuf/ProtoUtils.java
+++ b/protobuf/src/main/java/io/grpc/protobuf/ProtoUtils.java
@@ -43,6 +43,7 @@ public final class ProtoUtils {
    *
    * @since 1.16.0
    */
+  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1787")
   public static void setExtensionRegistry(ExtensionRegistry registry) {
     ProtoLiteUtils.setExtensionRegistry(registry);
   }