diff --git a/src/evalfunc.c b/src/evalfunc.c
index d6fb03e..287ca3c 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3932,6 +3932,11 @@
 	s = tv_get_string(&argvars[0]);
 	use_string = TRUE;
     }
+    if (s == NULL)
+    {
+	semsg(_(e_invarg2), "NULL");
+	return;
+    }
 
     if ((use_string && vim_strchr(s, AUTOLOAD_CHAR) == NULL) || is_funcref)
     {