diff --git a/builtin/merge-base.c b/builtin/merge-base.c
index e3f8da13b6..ecc4268d43 100644
--- a/builtin/merge-base.c
+++ b/builtin/merge-base.c
@@ -114,26 +114,18 @@ static int handle_is_ancestor(int argc, const char **argv)
 static int handle_fork_point(int argc, const char **argv)
 {
 	struct object_id oid;
-	char *refname;
 	struct commit *derived, *fork_point;
 	const char *commitname;
 
-	switch (dwim_ref(argv[0], strlen(argv[0]), &oid, &refname)) {
-	case 0:
-		die("No such ref: '%s'", argv[0]);
-	case 1:
-		break; /* good */
-	default:
-		die("Ambiguous refname: '%s'", argv[0]);
-	}
-
 	commitname = (argc == 2) ? argv[1] : "HEAD";
 	if (get_oid(commitname, &oid))
 		die("Not a valid object name: '%s'", commitname);
 
 	derived = lookup_commit_reference(the_repository, &oid);
 
-	fork_point = get_fork_point(refname, derived);
+	fork_point = NULL;
+	if (get_fork_point(argv[0], derived, &fork_point) < 0)
+		return 1;
 
 	if (!fork_point)
 		return 1;
diff --git a/builtin/rebase.c b/builtin/rebase.c
index e755087b0f..782cf5a890 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1980,8 +1980,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		struct commit *head =
 			lookup_commit_reference(the_repository,
 						&options.orig_head);
-		options.restrict_revision =
-			get_fork_point(options.upstream_name, head);
+		options.restrict_revision = NULL;
+		if (get_fork_point(options.upstream_name, head, &options.restrict_revision) < 0)
+			die(_("could not get fork point"));
 	}
 
 	if (repo_read_index(the_repository) < 0)
diff --git a/commit.c b/commit.c
index 434ec030d6..874bc0cdf1 100644
--- a/commit.c
+++ b/commit.c
@@ -920,19 +920,25 @@ static int collect_one_reflog_ent(struct object_id *ooid, struct object_id *noid
 	return 0;
 }
 
-struct commit *get_fork_point(const char *refname, struct commit *commit)
+int get_fork_point(const char *refname, struct commit *commit, struct commit **fork_point)
 {
 	struct object_id oid;
 	struct rev_collect revs;
 	struct commit_list *bases;
 	int i;
-	struct commit *ret = NULL;
+	char *full_refname;
+
+	if (dwim_unique_ref(refname, strlen(refname), &oid, &full_refname) < 0) {
+		free(full_refname);
+		return -1;
+	}
+
 
 	memset(&revs, 0, sizeof(revs));
 	revs.initial = 1;
-	for_each_reflog_ent(refname, collect_one_reflog_ent, &revs);
+	for_each_reflog_ent(full_refname, collect_one_reflog_ent, &revs);
 
-	if (!revs.nr && !get_oid(refname, &oid))
+	if (!revs.nr && !get_oid(full_refname, &oid))
 		add_one_commit(&oid, &revs);
 
 	for (i = 0; i < revs.nr; i++)
@@ -954,11 +960,12 @@ struct commit *get_fork_point(const char *refname, struct commit *commit)
 	if (revs.nr <= i)
 		goto cleanup_return;
 
-	ret = bases->item;
+	*fork_point = bases->item;
 
 cleanup_return:
+	free(full_refname);
 	free_commit_list(bases);
-	return ret;
+	return 0;
 }
 
 static const char gpg_sig_header[] = "gpgsig";
diff --git a/commit.h b/commit.h
index 221cdaa34b..d79a8eab48 100644
--- a/commit.h
+++ b/commit.h
@@ -240,7 +240,7 @@ int register_commit_graft(struct repository *r, struct commit_graft *, int);
 void prepare_commit_graft(struct repository *r);
 struct commit_graft *lookup_commit_graft(struct repository *r, const struct object_id *oid);
 
-struct commit *get_fork_point(const char *refname, struct commit *commit);
+int get_fork_point(const char *refname, struct commit *commit, struct commit **fork_point);
 
 /* largest positive number a signed 32-bit integer can contain */
 #define INFINITE_DEPTH 0x7fffffff
diff --git a/refs.c b/refs.c
index 1ab0bb54d3..853e45a6a3 100644
--- a/refs.c
+++ b/refs.c
@@ -639,6 +639,20 @@ int dwim_ref(const char *str, int len, struct object_id *oid, char **ref)
 	return repo_dwim_ref(the_repository, str, len, oid, ref);
 }
 
+int dwim_unique_ref(const char* str, int len, struct object_id *oid, char **ref)
+{
+	struct object_id discard;
+	switch (dwim_ref(str, len, &discard, ref)) {
+	case 0:
+		return error(_("no such ref: '%s'"), str);
+	case 1:
+		break; /* good */
+	default:
+		return error(_("ambiguous refname: '%s'"), str);
+	}
+	return 0;
+}
+
 int expand_ref(struct repository *repo, const char *str, int len,
 	       struct object_id *oid, char **ref)
 {
diff --git a/refs.h b/refs.h
index 730d05ad91..7aa348052b 100644
--- a/refs.h
+++ b/refs.h
@@ -154,6 +154,8 @@ int repo_dwim_log(struct repository *r, const char *str, int len, struct object_
 int dwim_ref(const char *str, int len, struct object_id *oid, char **ref);
 int dwim_log(const char *str, int len, struct object_id *oid, char **ref);
 
+int dwim_unique_ref(const char* str, int len, struct object_id *oid, char **ref);
+
 /*
  * A ref_transaction represents a collection of reference updates that
  * should succeed or fail together.
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 78851b9a2a..5b09aecd13 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -47,11 +47,31 @@ test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
 test_rebase 'G F C B A' --no-fork-point --keep-base
+
 test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F E D B A' --fork-point master
+
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D master
+
 test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base master
+
 test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C E D B A' master
+
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C D B A' --onto D master
+
 test_rebase 'G F C B A' --keep-base refs/heads/master
+test_rebase 'G F C B A' --keep-base master
+
+test_expect_success "git rebase --fork-point with ambigous refname" "
+	git checkout master &&
+	git checkout -b one &&
+	git checkout side &&
+	git tag one &&
+	test_must_fail git rebase --fork-point --onto D one
+"
 
 test_done
