diff --git a/qemu/scripts/qapi/common.py b/qemu/scripts/qapi/common.py
index 8dab62f5..6a3ea452 100644
--- a/qemu/scripts/qapi/common.py
+++ b/qemu/scripts/qapi/common.py
@@ -1876,7 +1876,7 @@ def mcgen(code, **kwds):
 
 
 def guardname(filename):
-    return c_name(filename, protect=False).upper()
+    return re.sub(r'[^A-Za-z0-9_]', '_', filename).upper()
 
 
 def guardstart(name):