diff --git a/C/scanner.c b/C/scanner.c
index 1bb8c89d4..a5bb025f9 100644
--- a/C/scanner.c
+++ b/C/scanner.c
@@ -1393,7 +1393,8 @@ Yap_clean_tokenizer(TokEntry *tokstart, VarEntry *vartable, VarEntry *anonvartab
   LOCAL_Comments = TermNil;
   LOCAL_CommentsNextChar = LOCAL_CommentsTail = NULL;
   free(LOCAL_CommentsBuff);
-  LOCAL_CommentsBuff = NULL;
+  if (LOCAL_CommentsBuff)
+    LOCAL_CommentsBuff = NULL;
   LOCAL_CommentsBuffLim = 0;
 }