diff --git a/app/models/project.rb b/app/models/project.rb
index 5d0e61ecaa7..e569f325068 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -1032,6 +1032,8 @@ class Project < ActiveRecord::Base
   end
 
   def fork_source
+    return nil unless forked?
+
     forked_from_project || fork_network&.root_project
   end
 
diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index 987be8e8b46..4d10df410ab 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -1951,6 +1951,10 @@ describe Project do
 
         expect(second_fork.fork_source).to eq(project)
       end
+
+      it 'returns nil if it is the root of the fork network' do
+        expect(project.fork_source).to be_nil
+      end
     end
 
     describe '#lfs_storage_project' do