diff --git a/CHANGELOG b/CHANGELOG
index f3fc54219e4..9b0c6ba4609 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -23,6 +23,7 @@ v 8.7.0 (unreleased)
   - Handle nil descriptions in Slack issue messages (Stan Hu)
   - API: Expose open_issues_count, closed_issues_count, open_merge_requests_count for labels (Robert Schilling)
   - Add default scope to projects to exclude projects pending deletion
+  - Allow to close merge requests which source projects(forks) are deleted.
   - Ensure empty recipients are rejected in BuildsEmailService
   - API: Ability to filter milestones by state `active` and `closed` (Robert Schilling)
   - API: Fix milestone filtering by `iid` (Robert Schilling)
diff --git a/app/models/commit.rb b/app/models/commit.rb
index d09876a07d9..11ecfcace14 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -150,13 +150,11 @@ class Commit
   end
 
   def hook_attrs(with_changed_files: false)
-    path_with_namespace = project.path_with_namespace
-
     data = {
       id: id,
       message: safe_message,
       timestamp: committed_date.xmlschema,
-      url: "#{Gitlab.config.gitlab.url}/#{path_with_namespace}/commit/#{id}",
+      url: commit_url,
       author: {
         name: author_name,
         email: author_email
@@ -170,6 +168,10 @@ class Commit
     data
   end
 
+  def commit_url
+    project.present? ? "#{Gitlab.config.gitlab.url}/#{project.path_with_namespace}/commit/#{id}" : ""
+  end
+
   # Discover issues should be closed when this commit is pushed to a project's
   # default branch.
   def closes_issues(current_user = self.committer)
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index bf185cb5dd8..e410febdfff 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -128,7 +128,7 @@ class MergeRequest < ActiveRecord::Base
   validates :target_project, presence: true
   validates :target_branch, presence: true
   validates :merge_user, presence: true, if: :merge_when_build_succeeds?
-  validate :validate_branches
+  validate :validate_branches, unless: :allow_broken
   validate :validate_fork
 
   scope :by_branch, ->(branch_name) { where("(source_branch LIKE :branch) OR (target_branch LIKE :branch)", branch: branch_name) }
@@ -218,7 +218,7 @@ class MergeRequest < ActiveRecord::Base
     end
 
     if opened? || reopened?
-      similar_mrs = self.target_project.merge_requests.where(source_branch: source_branch, target_branch: target_branch, source_project_id: source_project.id).opened
+      similar_mrs = self.target_project.merge_requests.where(source_branch: source_branch, target_branch: target_branch, source_project_id: source_project.try(:id)).opened
       similar_mrs = similar_mrs.where('id not in (?)', self.id) if self.id
       if similar_mrs.any?
         errors.add :validate_branches,
@@ -345,7 +345,7 @@ class MergeRequest < ActiveRecord::Base
 
   def hook_attrs
     attrs = {
-      source: source_project.hook_attrs,
+      source: source_project.try(:hook_attrs),
       target: target_project.hook_attrs,
       last_commit: nil,
       work_in_progress: work_in_progress?
diff --git a/spec/controllers/projects/merge_requests_controller_spec.rb b/spec/controllers/projects/merge_requests_controller_spec.rb
index 75e6b6f45a7..c54e83339a1 100644
--- a/spec/controllers/projects/merge_requests_controller_spec.rb
+++ b/spec/controllers/projects/merge_requests_controller_spec.rb
@@ -157,6 +157,34 @@ describe Projects::MergeRequestsController do
     end
   end
 
+  describe 'PUT #update' do
+    context 'there is no source project' do
+      let(:project)       { create(:project) }
+      let(:fork_project)  { create(:forked_project_with_submodules) }
+      let(:merge_request) { create(:merge_request, source_project: fork_project, source_branch: 'add-submodule-version-bump', target_branch: 'master', target_project: project) }
+
+      before do
+        fork_project.build_forked_project_link(forked_to_project_id: fork_project.id, forked_from_project_id: project.id)
+        fork_project.save
+        merge_request.reload
+        fork_project.destroy
+      end
+
+      it 'closes MR without errors' do
+        post :update,
+            namespace_id: project.namespace.path,
+            project_id: project.path,
+            id: merge_request.iid,
+            merge_request: {
+              state_event: 'close'
+            }
+
+        expect(response).to redirect_to([merge_request.target_project.namespace.becomes(Namespace), merge_request.target_project, merge_request])
+        expect(merge_request.reload.closed?).to be_truthy
+      end
+    end
+  end
+
   describe "DELETE #destroy" do
     it "denies access to users unless they're admin or project owner" do
       delete :destroy, namespace_id: project.namespace.path, project_id: project.path, id: merge_request.iid