diff --git a/builtin-show-ref.c b/builtin-show-ref.c
index 65051d14fd..a323633e29 100644
--- a/builtin-show-ref.c
+++ b/builtin-show-ref.c
@@ -86,6 +86,9 @@ match:
 			    sha1_to_hex(sha1));
 		if (obj->type == OBJ_TAG) {
 			obj = deref_tag(obj, refname, 0);
+			if (!obj)
+				die("git-show-ref: bad tag at ref %s (%s)", refname,
+				    sha1_to_hex(sha1));
 			hex = find_unique_abbrev(obj->sha1, abbrev);
 			printf("%s %s^{}\n", hex, refname);
 		}
diff --git a/merge-recursive.c b/merge-recursive.c
index dd52342539..55ef76f5a5 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1673,6 +1673,8 @@ static struct commit *get_ref(const char *ref)
 	if (get_sha1(ref, sha1))
 		die("Could not resolve ref '%s'", ref);
 	object = deref_tag(parse_object(sha1), ref, strlen(ref));
+	if (!object)
+		return NULL;
 	if (object->type == OBJ_TREE)
 		return make_virtual_commit((struct tree*)object,
 			better_branch_name(ref));
diff --git a/sha1_name.c b/sha1_name.c
index be8489e4e5..ed3c867d6a 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -578,8 +578,11 @@ static int handle_one_ref(const char *path,
 	struct object *object = parse_object(sha1);
 	if (!object)
 		return 0;
-	if (object->type == OBJ_TAG)
+	if (object->type == OBJ_TAG) {
 		object = deref_tag(object, path, strlen(path));
+		if (!object)
+			return 0;
+	}
 	if (object->type != OBJ_COMMIT)
 		return 0;
 	insert_by_date((struct commit *)object, list);
diff --git a/shallow.c b/shallow.c
index dbd9f5ad0a..212e62b77c 100644
--- a/shallow.c
+++ b/shallow.c
@@ -56,7 +56,7 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
 			if (i < heads->nr) {
 				commit = (struct commit *)
 					deref_tag(heads->objects[i++].item, NULL, 0);
-				if (commit->object.type != OBJ_COMMIT) {
+				if (!commit || commit->object.type != OBJ_COMMIT) {
 					commit = NULL;
 					continue;
 				}
diff --git a/upload-pack.c b/upload-pack.c
index 51e3ec49d1..eaea9990e9 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -575,7 +575,8 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 	}
 	if (o->type == OBJ_TAG) {
 		o = deref_tag(o, refname, 0);
-		packet_write(1, "%s %s^{}\n", sha1_to_hex(o->sha1), refname);
+		if (o)
+			packet_write(1, "%s %s^{}\n", sha1_to_hex(o->sha1), refname);
 	}
 	return 0;
 }