diff --git a/DFReader.py b/DFReader.py
index 2fc14d2dd..5b629276d 100644
--- a/DFReader.py
+++ b/DFReader.py
@@ -594,7 +594,8 @@ def metadata_tree(self,verbose=False):
                     mavutil.mavlink.MAV_TYPE_SUBMARINE : "Sub",
                     mavutil.mavlink.MAV_TYPE_AIRSHIP : "Blimp",
                     }
-        if self.parent.mav_type in mapping:
+        if self.parent.mav_type not in mapping:
+            return None
             path = self.dot_mavproxy(os.path.join("LogMessages","%s.xml" % mapping[self.parent.mav_type]))
         else:
             return None