diff --git a/pyperf/_metadata.py b/pyperf/_metadata.py
index 245ac64b..8138983e 100644
--- a/pyperf/_metadata.py
+++ b/pyperf/_metadata.py
@@ -14,10 +14,8 @@ def _common_metadata(metadatas):
 
     metadata = dict(metadatas[0])
     for run_metadata in metadatas[1:]:
-        for key in set(metadata) - set(run_metadata):
-            del metadata[key]
-        for key in set(run_metadata) & set(metadata):
-            if run_metadata[key] != metadata[key]:
+        for key in list(metadata):
+            if metadata[key] != run_metadata.get(key,None):
                 del metadata[key]
     return metadata