diff --git a/scripts/decodetree.py b/scripts/decodetree.py
index 41301c84aa..277f9a9bba 100755
--- a/scripts/decodetree.py
+++ b/scripts/decodetree.py
@@ -972,6 +972,7 @@ def main():
     global input_file
     global insnwidth
     global insntype
+    global insnmask
 
     decode_function = 'decode'
     decode_scope = 'static '