diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index ad32c32..35a3821 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -188,10 +188,17 @@
     size_t	len;
     char_u	*buf;
     isntype_T	isn = ISN_EXEC;
+    char	*cmd = eap->cmdidx == CMD_lockvar ? "lockvar" : "unlockvar";
 
     if (cctx->ctx_skip == SKIP_YES)
 	return OK;
 
+    if (*p == NUL)
+    {
+	semsg(_(e_argument_required_for_str), cmd);
+	return FAIL;
+    }
+
     // Cannot use :lockvar and :unlockvar on local variables.
     if (p[1] != ':')
     {
@@ -223,8 +230,6 @@
 	ret = FAIL;
     else
     {
-	char *cmd = eap->cmdidx == CMD_lockvar ? "lockvar" : "unlockvar";
-
 	if (deep < 0)
 	    vim_snprintf((char *)buf, len, "%s! %s", cmd, p);
 	else