diff --git a/builtin/merge.c b/builtin/merge.c
index 2870a6af6f..1712b93e45 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1169,9 +1169,12 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		die(_("You cannot combine --no-ff with --ff-only."));
 
 	if (!abort_current_merge) {
-		if (!argc && default_to_upstream)
-			argc = setup_with_upstream(&argv);
-		else if (argc == 1 && !strcmp(argv[0], "-"))
+		if (!argc) {
+			if (default_to_upstream)
+				argc = setup_with_upstream(&argv);
+			else
+				die(_("No commit specified and merge.defaultToUpstream not set."));
+		} else if (argc == 1 && !strcmp(argv[0], "-"))
 			argv[0] = "@{-1}";
 	}
 	if (!argc)