diff --git a/app/models/user.rb b/app/models/user.rb
index bb8d5d24b3b2f221ced81f91ee8fec5c056f64ec..3230a18662039fa227f521e92f19c0a6ee74338f 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -197,6 +197,8 @@ def update_tracked_fields!(request)
   has_many :snippets,                 dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :notes,                    dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :issues,                   dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
+  has_many :legacy_assigned_merge_requests, class_name: 'MergeRequest', dependent: :nullify, foreign_key: :assignee_id # rubocop:disable Cop/ActiveRecordDependent
+  has_many :updated_merge_requests, class_name: 'MergeRequest', dependent: :nullify, foreign_key: :updated_by_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :updated_issues, class_name: 'Issue', dependent: :nullify, foreign_key: :updated_by_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :closed_issues, class_name: 'Issue', dependent: :nullify, foreign_key: :closed_by_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :merge_requests,           dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
diff --git a/spec/services/users/destroy_service_spec.rb b/spec/services/users/destroy_service_spec.rb
index b32599d4af89700571931a414e54edf1e2bd7c0d..c8ea7f704e222211e7ce3a303ca54009b656f1bb 100644
--- a/spec/services/users/destroy_service_spec.rb
+++ b/spec/services/users/destroy_service_spec.rb
@@ -407,6 +407,21 @@
         expect(issue.updated_by).to be_nil
         expect(resource_label_event.user).to be_nil
       end
+
+      it 'nullifies assigned_merge_requests, last_updated_merge_requests' do
+        merge_request = create(:merge_request, source_project: project, target_project: project,
+                                               assignee: other_user, updated_by: other_user, merge_user: other_user)
+
+        described_class.new(user).execute(other_user, skip_authorization: true)
+
+        merge_request.reload
+
+        aggregate_failures do
+          expect(merge_request.updated_by).to be_nil
+          expect(merge_request.assignee).to be_nil
+          expect(merge_request.assignee_id).to be_nil
+        end
+      end
     end
   end