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
@@ -56,6 +56,25 @@ class TestCreatePullRequestApi(object):
             assert_error(id_, expected, given=response.body)
 
     @pytest.mark.backends("git", "hg")
+    @pytest.mark.parametrize('source_ref', [
+        'bookmarg:default:initial'
+    ])
+    def test_create_with_wrong_refs_data(self, backend, source_ref):
+
+        data = self._prepare_data(backend)
+        data['source_ref'] = source_ref
+
+        id_, params = build_data(
+            self.apikey_regular, 'create_pull_request', **data)
+
+        response = api_call(self.app, params)
+
+        expected = "Ref `{}` type is not allowed. " \
+                   "Only:['bookmark', 'book', 'tag', 'branch'] " \
+                   "are possible.".format(source_ref)
+        assert_error(id_, expected, given=response.body)
+
+    @pytest.mark.backends("git", "hg")
     def test_create_with_correct_data(self, backend):
         data = self._prepare_data(backend)
         RepoModel().revoke_user_permission(
diff --git a/rhodecode/api/tests/test_utils.py b/rhodecode/api/tests/test_utils.py
--- a/rhodecode/api/tests/test_utils.py
+++ b/rhodecode/api/tests/test_utils.py
@@ -84,11 +84,11 @@ class TestResolveRefOrError(object):
 
     def test_non_supported_refs(self):
         repo = Mock()
-        ref = 'ancestor:ref'
+        ref = 'bookmark:ref'
         with pytest.raises(JSONRPCError) as excinfo:
             utils.resolve_ref_or_error(ref, repo)
         expected_message = (
-            'The specified value:ancestor:`ref` does not exist, or is not allowed.')
+            'The specified value:bookmark:`ref` does not exist, or is not allowed.')
         assert excinfo.value.message == expected_message
 
     def test_branch_is_not_found(self):
diff --git a/rhodecode/api/utils.py b/rhodecode/api/utils.py
--- a/rhodecode/api/utils.py
+++ b/rhodecode/api/utils.py
@@ -388,7 +388,19 @@ def get_commit_or_error(ref, repo):
         raise JSONRPCError('Ref `{ref}` does not exist'.format(ref=ref))
 
 
-def resolve_ref_or_error(ref, repo):
+def _get_ref_hash(repo, type_, name):
+    vcs_repo = repo.scm_instance()
+    if type_ in ['branch'] and vcs_repo.alias in ('hg', 'git'):
+        return vcs_repo.branches[name]
+    elif type_ in ['bookmark', 'book'] and vcs_repo.alias == 'hg':
+        return vcs_repo.bookmarks[name]
+    else:
+        raise ValueError()
+
+
+def resolve_ref_or_error(ref, repo, allowed_ref_types=None):
+    allowed_ref_types = allowed_ref_types or ['bookmark', 'book', 'tag', 'branch']
+
     def _parse_ref(type_, name, hash_=None):
         return type_, name, hash_
 
@@ -399,6 +411,12 @@ def resolve_ref_or_error(ref, repo):
             'Ref `{ref}` given in a wrong format. Please check the API'
             ' documentation for more details'.format(ref=ref))
 
+    if ref_type not in allowed_ref_types:
+        raise JSONRPCError(
+            'Ref `{ref}` type is not allowed. '
+            'Only:{allowed_refs} are possible.'.format(
+                ref=ref, allowed_refs=allowed_ref_types))
+
     try:
         ref_hash = ref_hash or _get_ref_hash(repo, ref_type, ref_name)
     except (KeyError, ValueError):
@@ -429,13 +447,3 @@ def _get_commit_dict(
         "raw_diff": raw_diff,
         "stats": stats
     }
-
-
-def _get_ref_hash(repo, type_, name):
-    vcs_repo = repo.scm_instance()
-    if type_ == 'branch' and vcs_repo.alias in ('hg', 'git'):
-        return vcs_repo.branches[name]
-    elif type_ == 'bookmark' and vcs_repo.alias == 'hg':
-        return vcs_repo.bookmarks[name]
-    else:
-        raise ValueError()
diff --git a/rhodecode/model/pull_request.py b/rhodecode/model/pull_request.py
--- a/rhodecode/model/pull_request.py
+++ b/rhodecode/model/pull_request.py
@@ -129,6 +129,8 @@ class PullRequestModel(BaseModel):
             'This pull request cannot be updated because the source '
             'reference is missing.'),
     }
+    REF_TYPES = ['bookmark', 'book', 'tag', 'branch']
+    UPDATABLE_REF_TYPES = ['bookmark', 'book', 'branch']
 
     def __get_pull_request(self, pull_request):
         return self._get_instance((
@@ -671,7 +673,7 @@ class PullRequestModel(BaseModel):
 
     def has_valid_update_type(self, pull_request):
         source_ref_type = pull_request.source_ref_parts.type
-        return source_ref_type in ['book', 'branch', 'tag']
+        return source_ref_type in self.REF_TYPES
 
     def update_commits(self, pull_request):
         """
@@ -751,7 +753,7 @@ class PullRequestModel(BaseModel):
             pull_request_version = pull_request
 
         try:
-            if target_ref_type in ('tag', 'branch', 'book'):
+            if target_ref_type in self.REF_TYPES:
                 target_commit = target_repo.get_commit(target_ref_name)
             else:
                 target_commit = target_repo.get_commit(target_ref_id)
@@ -1326,7 +1328,7 @@ class PullRequestModel(BaseModel):
         return merge_state
 
     def _refresh_reference(self, reference, vcs_repository):
-        if reference.type in ('branch', 'book'):
+        if reference.type in self.UPDATABLE_REF_TYPES:
             name_or_id = reference.name
         else:
             name_or_id = reference.commit_id