diff --git a/vm/nga-python/retro.py b/vm/nga-python/retro.py
index 0c73f27..5c6cb3d 100644
--- a/vm/nga-python/retro.py
+++ b/vm/nga-python/retro.py
@@ -114,7 +114,8 @@ class Retro:
         header = self.memory[2]
         while header != 0:
             named = self.extract_string(header + 3)
-            Dictionary[named] = header
+            if not named in Dictionary:
+                Dictionary[named] = header
             header = self.memory[header]
         return Dictionary