1 files changed, 2 insertions, 5 deletions
diff --git a/java/core/src/main/java/com/google/protobuf/Extension.java b/java/core/src/main/java/com/google/protobuf/Extension.java
index 08ec5b45..5df12e64 100644
--- a/java/core/src/main/java/com/google/protobuf/Extension.java
+++ b/java/core/src/main/java/com/google/protobuf/Extension.java
@@ -58,10 +58,7 @@ public abstract class Extension<ContainingType extends MessageLite, Type>
     PROTO1,
   }
 
-  protected ExtensionType getExtensionType() {
-    // TODO(liujisi): make this abstract after we fix proto1.
-    return ExtensionType.IMMUTABLE;
-  }
+  protected abstract ExtensionType getExtensionType();
 
   /**
    * Type of a message extension.
@@ -70,7 +67,7 @@ public abstract class Extension<ContainingType extends MessageLite, Type>
     PROTO1,
     PROTO2,
   }
-  
+
   /**
    * If the extension is a message extension (i.e., getLiteType() == MESSAGE),
    * returns the type of the message, otherwise undefined.