diff --git a/usr.bin/yacc/skeleton.c b/usr.bin/yacc/skeleton.c
index f765c912f5c8..c1263d9e2872 100644
--- a/usr.bin/yacc/skeleton.c
+++ b/usr.bin/yacc/skeleton.c
@@ -60,6 +60,7 @@ __FBSDID("$FreeBSD$");
 const char *banner[] =
 {
     "#include <stdlib.h>",
+    "#include <string.h>",
     "#ifndef lint",
     "#ifdef __unused",
     "__unused",
@@ -331,7 +332,10 @@ const char *body[] =
     "                YYPREFIX, yystate, yyn, yyrule[yyn]);",
     "#endif",
     "    yym = yylen[yyn];",
-    "    yyval = yyvsp[1-yym];",
+    "    if (yym)",
+    "        yyval = yyvsp[1-yym];",
+    "    else",
+    "    memset(&yyval, 0, sizeof yyval);",
     "    switch (yyn)",
     "    {",
     0