diff --git a/app/views/projects/issues/show.html.haml b/app/views/projects/issues/show.html.haml
index 715c36fa9aa632d6e59f8ab41a8e915b626211d6..d55afee4523585652a55ecc0a8cd2442593584e5 100644
--- a/app/views/projects/issues/show.html.haml
+++ b/app/views/projects/issues/show.html.haml
@@ -79,7 +79,7 @@
 
     = render_if_exists 'projects/issues/related_issues'
 
-    #js-related-merge-requests{ data: { endpoint: expose_url(api_v4_projects_issues_related_merge_requests_path(id: @project.id, issue_iid: @issue.iid)), project_namespace: @project.namespace.path, project_path: @project.path } }
+    #js-related-merge-requests{ data: { endpoint: expose_path(api_v4_projects_issues_related_merge_requests_path(id: @project.id, issue_iid: @issue.iid)), project_namespace: @project.namespace.path, project_path: @project.path } }
 
     - if can?(current_user, :download_code, @project)
       #related-branches{ data: { url: related_branches_project_issue_path(@project, @issue) } }
diff --git a/changelogs/unreleased/sh-fix-related-merge-requests-path.yml b/changelogs/unreleased/sh-fix-related-merge-requests-path.yml
new file mode 100644
index 0000000000000000000000000000000000000000..4b4108feda4e056a2e46c13fa69729143af78a68
--- /dev/null
+++ b/changelogs/unreleased/sh-fix-related-merge-requests-path.yml
@@ -0,0 +1,5 @@
+---
+title: Use a path for the related merge requests endpoint
+merge_request: 28171
+author:
+type: fixed
diff --git a/lib/api/helpers/related_resources_helpers.rb b/lib/api/helpers/related_resources_helpers.rb
index 793ae11b41d224f3fd83e58a781af2fe22fec761..9cdde25fe4e1d1c3967f5d1dcf9a56e907de9b7f 100644
--- a/lib/api/helpers/related_resources_helpers.rb
+++ b/lib/api/helpers/related_resources_helpers.rb
@@ -13,6 +13,10 @@ module API
         available?(:merge_requests, project, options[:current_user])
       end
 
+      def expose_path(path)
+        Gitlab::Utils.append_path(Gitlab.config.gitlab.relative_url_root, path)
+      end
+
       def expose_url(path)
         url_options = Gitlab::Application.routes.default_url_options
         protocol, host, port, script_name = url_options.values_at(:protocol, :host, :port, :script_name)
diff --git a/spec/lib/api/helpers/related_resources_helpers_spec.rb b/spec/lib/api/helpers/related_resources_helpers_spec.rb
index 66af7f81535db423f7197a0fb7886b97f7d4cb05..99fe8795d917101fd43876af5b867fb3c84cb309 100644
--- a/spec/lib/api/helpers/related_resources_helpers_spec.rb
+++ b/spec/lib/api/helpers/related_resources_helpers_spec.rb
@@ -5,6 +5,40 @@ describe API::Helpers::RelatedResourcesHelpers do
     Class.new.include(described_class).new
   end
 
+  describe '#expose_path' do
+    let(:path) { '/api/v4/awesome_endpoint' }
+
+    context 'empty relative URL root' do
+      before do
+        stub_config_setting(relative_url_root: '')
+      end
+
+      it 'returns the existing path' do
+        expect(helpers.expose_path(path)).to eq(path)
+      end
+    end
+
+    context 'slash relative URL root' do
+      before do
+        stub_config_setting(relative_url_root: '/')
+      end
+
+      it 'returns the existing path' do
+        expect(helpers.expose_path(path)).to eq(path)
+      end
+    end
+
+    context 'with relative URL root' do
+      before do
+        stub_config_setting(relative_url_root: '/gitlab/root')
+      end
+
+      it 'returns the existing path' do
+        expect(helpers.expose_path(path)).to eq("/gitlab/root" + path)
+      end
+    end
+  end
+
   describe '#expose_url' do
     let(:path) { '/api/v4/awesome_endpoint' }
     subject(:url) { helpers.expose_url(path) }