diff --git a/usr.bin/yacc/yyfix.sh b/usr.bin/yacc/yyfix.sh
index 29085f9861f..d983df678e7 100644
--- a/usr.bin/yacc/yyfix.sh
+++ b/usr.bin/yacc/yyfix.sh
@@ -37,6 +37,11 @@ OLDYACC="yyexca yyact yypact yypgo yyr1 yyr2 yychk yydef"
 NEWYACC="yylhs yylen yydefred yydgoto yysindex yyrindex yygindex \
 	 yytable yycheck"
 
+if [ $# -eq 0 ]; then
+	echo "usage: $0 file [tables]" >&2
+	exit 1
+fi
+
 file=$1
 >$file
 shift