diff --git a/util/topgen/LLlex.c b/util/topgen/LLlex.c
index 646664c0b..3cd613abc 100644
--- a/util/topgen/LLlex.c
+++ b/util/topgen/LLlex.c
@@ -54,7 +54,7 @@ LLlex() {
 			else c = getc(input);
                 }
 		else {
-			ungetc(c, stdin);
+			ungetc(c, input);
 			c = '/';
 			break;
 		}