diff --git a/builtin/bisect.c b/builtin/bisect.c
index 798e28f501..2672cbe5d1 100644
--- a/builtin/bisect.c
+++ b/builtin/bisect.c
@@ -663,6 +663,11 @@ static int bisect_successful(struct bisect_terms *terms)
 
 	refs_read_ref(get_main_ref_store(the_repository), bad_ref, &oid);
 	commit = lookup_commit_reference_by_name(bad_ref);
+	if (!commit) {
+		error(_("could not find commit for '%s'"), bad_ref);
+		free(bad_ref);
+		return BISECT_FAILED;
+	}
 	repo_format_commit_message(the_repository, commit, "%s", &commit_name,
 				   &pp);