diff --git a/builtin/clone.c b/builtin/clone.c
index f044a8c27f542c94c0b7f2458de1590e0d02fae2..a35d62293a9c84abb1473a1962c7af1540ed5017 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -355,8 +355,11 @@ static void copy_alternates(struct strbuf *src, struct strbuf *dst,
 			continue;
 		}
 		abs_path = mkpathdup("%s/objects/%s", src_repo, line.buf);
-		normalize_path_copy(abs_path, abs_path);
-		add_to_alternates_file(abs_path);
+		if (!normalize_path_copy(abs_path, abs_path))
+			add_to_alternates_file(abs_path);
+		else
+			warning("skipping invalid relative alternate: %s/%s",
+				src_repo, line.buf);
 		free(abs_path);
 	}
 	strbuf_release(&line);