diff --git a/snippets/c-lang-common/once b/snippets/c-lang-common/once
index f320e7d89..fa274d81b 100644
--- a/snippets/c-lang-common/once
+++ b/snippets/c-lang-common/once
@@ -2,7 +2,7 @@
 # name: #ifndef XXX; #define XXX; #endif
 # key: once
 # --
-#ifndef ${1:`(upcase (file-name-nondirectory (file-name-sans-extension (or (buffer-file-name) ""))))`_H}
+#ifndef ${1:`(upcase (replace-regexp-in-string "[^A-Za-z0-9_]" "_" (file-name-nondirectory (or (buffer-file-name)))))`}
 #define $1
 
 $0