diff --git a/rhodecode/api/tests/test_create_pull_request.py b/rhodecode/api/tests/test_create_pull_request.py
--- a/rhodecode/api/tests/test_create_pull_request.py
+++ b/rhodecode/api/tests/test_create_pull_request.py
@@ -94,6 +94,20 @@ class TestCreatePullRequestApi(object):
         assert pull_request.description == ''
 
     @pytest.mark.backends("git", "hg")
+    def test_create_with_empty_title(self, backend):
+        data = self._prepare_data(backend)
+        data.pop('title')
+        id_, params = build_data(
+            self.apikey_regular, 'create_pull_request', **data)
+        response = api_call(self.app, params)
+        result = response.json
+        pull_request_id = result['result']['pull_request_id']
+        pull_request = PullRequestModel().get(pull_request_id)
+        data['ref'] = backend.default_branch_name
+        title = '{source_repo}#{ref} to {target_repo}'.format(**data)
+        assert pull_request.title == title
+
+    @pytest.mark.backends("git", "hg")
     def test_create_with_reviewers_specified_by_names(
             self, backend, no_notifications):
         data = self._prepare_data(backend)
@@ -277,6 +291,7 @@ class TestCreatePullRequestApi(object):
         self.commit_ids = backend.create_master_repo(commits)
         self.source = backend.create_repo(heads=[source_head])
         self.target = backend.create_repo(heads=[target_head])
+
         data = {
             'source_repo': self.source.repo_name,
             'target_repo': self.target.repo_name,
diff --git a/rhodecode/api/views/pull_request_api.py b/rhodecode/api/views/pull_request_api.py
--- a/rhodecode/api/views/pull_request_api.py
+++ b/rhodecode/api/views/pull_request_api.py
@@ -608,7 +608,7 @@ def create_pull_request(
             [{'username': 'nick', 'reasons': ['original author'], 'mandatory': <bool>}]
     """
 
-    source_db_repo =  get_repo_or_error(source_repo)
+    source_db_repo = get_repo_or_error(source_repo)
     target_db_repo = get_repo_or_error(target_repo)
     if not has_superadmin_permission(apiuser):
         _perms = ('repository.admin', 'repository.write', 'repository.read',)
@@ -616,24 +616,29 @@ def create_pull_request(
 
     full_source_ref = resolve_ref_or_error(source_ref, source_db_repo)
     full_target_ref = resolve_ref_or_error(target_ref, target_db_repo)
+
+    source_scm = source_db_repo.scm_instance()
+    target_scm = target_db_repo.scm_instance()
+
     source_commit = get_commit_or_error(full_source_ref, source_db_repo)
     target_commit = get_commit_or_error(full_target_ref, target_db_repo)
-    source_scm = source_db_repo.scm_instance()
-    target_scm = target_db_repo.scm_instance()
+
+    ancestor = source_scm.get_common_ancestor(
+        source_commit.raw_id, target_commit.raw_id, target_scm)
+    if not ancestor:
+        raise JSONRPCError('no common ancestor found')
+
+    # recalculate target ref based on ancestor
+    target_ref_type, target_ref_name, __ = full_target_ref.split(':')
+    full_target_ref = ':'.join((target_ref_type, target_ref_name, ancestor))
 
     commit_ranges = target_scm.compare(
         target_commit.raw_id, source_commit.raw_id, source_scm,
         merge=True, pre_load=[])
 
-    ancestor = target_scm.get_common_ancestor(
-        target_commit.raw_id, source_commit.raw_id, source_scm)
-
     if not commit_ranges:
         raise JSONRPCError('no commits found')
 
-    if not ancestor:
-        raise JSONRPCError('no common ancestor found')
-
     reviewer_objects = Optional.extract(reviewers) or []
 
     if reviewer_objects:
@@ -674,6 +679,7 @@ def create_pull_request(
             source_ref=title_source_ref,
             target=target_repo
         )
+    description = Optional.extract(description)
 
     pull_request = PullRequestModel().create(
         created_by=apiuser.user_id,
@@ -684,7 +690,7 @@ def create_pull_request(
         revisions=[commit.raw_id for commit in reversed(commit_ranges)],
         reviewers=reviewers,
         title=title,
-        description=Optional.extract(description),
+        description=description,
         reviewer_data=reviewer_rules,
         auth_user=apiuser
     )