diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index 35a3821..93032d6 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -92,6 +92,12 @@
     int
 check_vim9_unlet(char_u *name)
 {
+    if (*name == NUL)
+    {
+	semsg(_(e_argument_required_for_str), "unlet");
+	return FAIL;
+    }
+
     if (name[1] != ':' || vim_strchr((char_u *)"gwtb", *name) == NULL)
     {
 	// "unlet s:var" is allowed in legacy script.