diff --git a/python/pydevSrc/src/com/jetbrains/python/debugger/IPyDebugProcess.java b/python/pydevSrc/src/com/jetbrains/python/debugger/IPyDebugProcess.java
index 7cc215ad9b03..991e8eca9c6b 100644
--- a/python/pydevSrc/src/com/jetbrains/python/debugger/IPyDebugProcess.java
+++ b/python/pydevSrc/src/com/jetbrains/python/debugger/IPyDebugProcess.java
@@ -30,7 +30,7 @@ public interface IPyDebugProcess extends PyFrameAccessor {
 
   void showConsole(PyThreadInfo thread);
 
-  void loadReferrers(PyReferringObjectsValue var, PyDebugCallback<XValueChildrenList> callback);
+  void loadReferrers(PyReferringObjectsValue var, PyDebugCallback<? super XValueChildrenList> callback);
 
   void suspendAllOtherThreads(PyThreadInfo thread);
 
diff --git a/python/src/com/jetbrains/python/debugger/PyDebugProcess.java b/python/src/com/jetbrains/python/debugger/PyDebugProcess.java
index e0c2fa9df699..a26fe84423df 100644
--- a/python/src/com/jetbrains/python/debugger/PyDebugProcess.java
+++ b/python/src/com/jetbrains/python/debugger/PyDebugProcess.java
@@ -995,7 +995,7 @@ public class PyDebugProcess extends XDebugProcess implements IPyDebugProcess, Pr
   }
 
   @Override
-  public void loadReferrers(PyReferringObjectsValue var, PyDebugCallback<XValueChildrenList> callback) {
+  public void loadReferrers(PyReferringObjectsValue var, PyDebugCallback<? super XValueChildrenList> callback) {
     try {
       final PyStackFrame frame = currentFrame();
       myDebugger.loadReferrers(frame.getThreadId(), frame.getFrameId(), var, callback);