diff --git a/rhodecode/tests/vcs/test_git.py b/rhodecode/tests/vcs/test_git.py
--- a/rhodecode/tests/vcs/test_git.py
+++ b/rhodecode/tests/vcs/test_git.py
@@ -566,7 +566,8 @@ TODO: To be written...
 
     def test_maybe_prepare_merge_workspace(self):
         workspace = self.repo._maybe_prepare_merge_workspace(
-            'pr2', Reference('branch', 'master', 'unused'))
+            'pr2', Reference('branch', 'master', 'unused'),
+            Reference('branch', 'master', 'unused'))
 
         assert os.path.isdir(workspace)
         workspace_repo = GitRepository(workspace)
@@ -574,12 +575,29 @@ TODO: To be written...
 
         # Calling it a second time should also succeed
         workspace = self.repo._maybe_prepare_merge_workspace(
-            'pr2', Reference('branch', 'master', 'unused'))
+            'pr2', Reference('branch', 'master', 'unused'),
+            Reference('branch', 'master', 'unused'))
+        assert os.path.isdir(workspace)
+
+    def test_maybe_prepare_merge_workspace_different_refs(self):
+        workspace = self.repo._maybe_prepare_merge_workspace(
+            'pr2', Reference('branch', 'master', 'unused'),
+            Reference('branch', 'develop', 'unused'))
+
+        assert os.path.isdir(workspace)
+        workspace_repo = GitRepository(workspace)
+        assert workspace_repo.branches == self.repo.branches
+
+        # Calling it a second time should also succeed
+        workspace = self.repo._maybe_prepare_merge_workspace(
+            'pr2', Reference('branch', 'master', 'unused'),
+            Reference('branch', 'develop', 'unused'))
         assert os.path.isdir(workspace)
 
     def test_cleanup_merge_workspace(self):
         workspace = self.repo._maybe_prepare_merge_workspace(
-            'pr3', Reference('branch', 'master', 'unused'))
+            'pr3', Reference('branch', 'master', 'unused'),
+            Reference('branch', 'master', 'unused'))
         self.repo.cleanup_merge_workspace('pr3')
 
         assert not os.path.exists(workspace)
diff --git a/rhodecode/tests/vcs/test_hg.py b/rhodecode/tests/vcs/test_hg.py
--- a/rhodecode/tests/vcs/test_hg.py
+++ b/rhodecode/tests/vcs/test_hg.py
@@ -552,18 +552,21 @@ TODO: To be written...
         assert commit.message == merge_message
 
     def test_maybe_prepare_merge_workspace(self):
-        workspace = self.repo._maybe_prepare_merge_workspace('pr2', 'unused')
+        workspace = self.repo._maybe_prepare_merge_workspace(
+            'pr2', 'unused', 'unused2')
 
         assert os.path.isdir(workspace)
         workspace_repo = MercurialRepository(workspace)
         assert workspace_repo.branches == self.repo.branches
 
         # Calling it a second time should also succeed
-        workspace = self.repo._maybe_prepare_merge_workspace('pr2', 'unused')
+        workspace = self.repo._maybe_prepare_merge_workspace(
+            'pr2', 'unused', 'unused2')
         assert os.path.isdir(workspace)
 
     def test_cleanup_merge_workspace(self):
-        workspace = self.repo._maybe_prepare_merge_workspace('pr3', 'unused')
+        workspace = self.repo._maybe_prepare_merge_workspace(
+            'pr3', 'unused', 'unused2')
         self.repo.cleanup_merge_workspace('pr3')
 
         assert not os.path.exists(workspace)
diff --git a/rhodecode/tests/vcs/test_hg_vcsserver_cache_invalidation.py b/rhodecode/tests/vcs/test_hg_vcsserver_cache_invalidation.py
--- a/rhodecode/tests/vcs/test_hg_vcsserver_cache_invalidation.py
+++ b/rhodecode/tests/vcs/test_hg_vcsserver_cache_invalidation.py
@@ -104,7 +104,7 @@ class TestMercurialRemoteRepoInvalidatio
         pr = PullRequestModel()
         workspace_id = pr._workspace_id(pull_request)
         shadow_repository_path = target_vcs._maybe_prepare_merge_workspace(
-            workspace_id, target_ref)
+            workspace_id, target_ref, source_ref)
         shadow_repo = target_vcs._get_shadow_instance(shadow_repository_path)
 
         # This will populate the cache of the mercurial repository object