diff --git a/extras/crystal.py b/extras/crystal.py
index 92d3375fa..ab58a19cd 100644
--- a/extras/crystal.py
+++ b/extras/crystal.py
@@ -1724,7 +1724,11 @@ class TrainerGroupParam(SingleByteParam):
 
 class MoveParam(SingleByteParam):
     def to_asm(self):
-        return moves[self.byte]
+        if self.byte in moves.keys():
+            return moves[self.byte]
+        else:
+            # this happens for move=0 (no move) in trainer headers
+            return str(self.byte)
 
 class MenuDataPointerParam(PointerLabelParam):
     #read menu data at the target site