Make sure we have the branch on the other project

app/models/project.rb

@@ -988,6 +988,17 @@ class Project < ActiveRecord::Base
     Gitlab::UploadsTransfer.new.rename_project(path_was, path, namespace.path)
   end
 
+  def fetch_ref(source_project, branch_name, ref)
+    repository.fetch_ref(
+      source_project.repository.path_to_repo,
+      "refs/heads/#{ref}",
+      "refs/heads/#{branch_name}"
+    )
+
+    repository.after_create_branch
+    repository.find_branch(branch_name)
+  end
+
   # Expires various caches before a project is renamed.
   def expire_caches_before_rename(old_path)
     repo = Repository.new(old_path, self)

app/services/create_branch_service.rb

@@ -7,15 +7,7 @@ class CreateBranchService < BaseService
     return failure if failure
 
     new_branch = if source_project != @project
-                   repository.fetch_ref(
-                     source_project.repository.path_to_repo,
-                     "refs/heads/#{ref}",
-                     "refs/heads/#{branch_name}"
-                   )
-
-                   repository.after_create_branch
-
-                   repository.find_branch(branch_name)
+                   @project.fetch_ref(source_project, branch_name, ref)
                  else
                    repository.add_branch(current_user, branch_name, ref)
                  end

app/services/files/base_service.rb

@@ -23,7 +23,7 @@ module Files
       validate
 
       # Create new branch if it different from source_branch
-      validate_target_branch if different_branch?
+      ensure_target_branch if different_branch?
 
       result = commit
       if result
@@ -71,6 +71,14 @@ module Files
       end
     end
 
+    def ensure_target_branch
+      validate_target_branch
+
+      if @source_project != project
+        @project.fetch_ref(@source_project, @target_branch, @source_branch)
+      end
+    end
+
     def validate_target_branch
       result = ValidateNewBranchService.new(project, current_user).
         execute(@target_branch)