diff --git a/utils/uf2conv.py b/utils/uf2conv.py
index bf9a357..ecd1c54 100755
--- a/utils/uf2conv.py
+++ b/utils/uf2conv.py
@@ -115,6 +115,7 @@ def writeFile(name, buf):
     print "Wrote %d bytes to %s." % (len(buf), name)
 
 def main():
+    global appstartaddr
     def error(msg):
         print msg
         sys.exit(1)
@@ -167,4 +168,4 @@ def main():
             writeFile(outbuf, d + "/NEW.UF2")
 
 if __name__ == "__main__":
-    main()
\ No newline at end of file
+    main()