diff --git a/Lib/pstats.py b/Lib/pstats.py
index bdbb27e..adaac5c 100644
--- a/Lib/pstats.py
+++ b/Lib/pstats.py
@@ -512,7 +512,8 @@
         new_callers[func] = caller
     for func, caller in source.iteritems():
         if func in new_callers:
-            new_callers[func] = caller + new_callers[func]
+            new_callers[func] = tuple([i[0] + i[1] for i in
+                                       zip(caller, new_callers[func])])
         else:
             new_callers[func] = caller
     return new_callers