diff --git a/builtin/replay.c b/builtin/replay.c
index 7998f6ed04..f48c5ed255 100644
--- a/builtin/replay.c
+++ b/builtin/replay.c
@@ -179,7 +179,12 @@ int cmd_replay(int argc, const char **argv, const char *prefix)
 
 		fprintf(stderr, "Rebasing %s...\r",
 			oid_to_hex(&commit->object.oid));
-		assert(commit->parents && !commit->parents->next);
+
+		if (!commit->parents)
+			die(_("replaying down to root commit is not supported yet!"));
+		if (commit->parents->next)
+			die(_("replaying merge commits is not supported yet!"));
+
 		base = commit->parents->item;
 
 		next_tree = repo_get_commit_tree(the_repository, commit);