break;
                                continue;
                        }
-                       if (read_ref(git_path("%s", path), sha1) < 0)
+                       if (read_ref(git_path("%s", path), sha1) < 0) {
+                               fprintf(stderr, "%s points nowhere!", path);
                                continue;
-                       if (!has_sha1_file(sha1))
+                       }
+                       if (!has_sha1_file(sha1)) {
+                               fprintf(stderr, "%s does not point to a valid "
+                                               "commit object!", path);
                                continue;
+                       }
                        retval = fn(path, sha1);
                        if (retval)
                                break;