diff --git a/lib/api/search.rb b/lib/api/search.rb
index d271923dbd6..30e68c5aac1 100644
--- a/lib/api/search.rb
+++ b/lib/api/search.rb
@@ -53,15 +53,14 @@ module API
         # EE, without having to modify this file directly.
       end
 
-      params :scope do |options|
-        scope_entities =
-          if Feature.enabled?(:users_search, default_enabled: true)
-            SCOPE_ENTITY
-          else
-            SCOPE_ENTITY.reject { |key, value| key == :users }
-          end
+      def check_users_search_allowed!
+        if Feature.disabled?(:users_search, default_enabled: true) && params[:scope].to_sym == :users
+          render_api_error!({ error: _("Scope not supported with disabled 'users_search' feature!") }, 400)
+        end
+      end
 
-        values = scope_entities.stringify_keys.slice(*options[:values]).keys
+      params :scope do |options|
+        values = SCOPE_ENTITY.stringify_keys.slice(*options[:values]).keys
 
         requires :scope,
           type: String,
@@ -81,6 +80,7 @@ module API
       end
       get do
         verify_search_scope!
+        check_users_search_allowed!
 
         present search, with: entity
       end
@@ -98,6 +98,7 @@ module API
       end
       get ':id/(-/)search' do
         verify_search_scope!
+        check_users_search_allowed!
 
         present search(group_id: user_group.id), with: entity
       end
@@ -114,6 +115,8 @@ module API
         use :pagination
       end
       get ':id/(-/)search' do
+        check_users_search_allowed!
+
         present search(project_id: user_project.id), with: entity
       end
     end
diff --git a/locale/gitlab.pot b/locale/gitlab.pot
index 5b192f4ccbc..5cc4942d150 100644
--- a/locale/gitlab.pot
+++ b/locale/gitlab.pot
@@ -6632,6 +6632,9 @@ msgstr ""
 msgid "Scope"
 msgstr ""
 
+msgid "Scope not supported with disabled 'users_search' feature!"
+msgstr ""
+
 msgid "Scroll down to <strong>Google Code Project Hosting</strong> and enable the switch on the right."
 msgstr ""
 
diff --git a/spec/requests/api/search_spec.rb b/spec/requests/api/search_spec.rb
index 0f539fb6c60..49672591b3b 100644
--- a/spec/requests/api/search_spec.rb
+++ b/spec/requests/api/search_spec.rb
@@ -81,10 +81,22 @@ describe API::Search do
         before do
           create(:user, name: 'billy')
 
-          get api('/search', user), scope: 'users', search: 'billy'
+          get api('/search', user), params: { scope: 'users', search: 'billy' }
         end
 
         it_behaves_like 'response is correct', schema: 'public_api/v4/user/basics'
+
+        context 'when users search feature is disabled' do
+          before do
+            allow(Feature).to receive(:disabled?).with(:users_search, default_enabled: true).and_return(true)
+
+            get api('/search', user), params: { scope: 'users', search: 'billy' }
+          end
+
+          it 'returns 400 error' do
+            expect(response).to have_gitlab_http_status(400)
+          end
+        end
       end
 
       context 'for snippet_titles scope' do
@@ -203,15 +215,27 @@ describe API::Search do
         it_behaves_like 'response is correct', schema: 'public_api/v4/milestones'
       end
 
-      context 'for user scope' do
+      context 'for users scope' do
         before do
           user = create(:user, name: 'billy')
           create(:group_member, :developer, user: user, group: group)
 
-          get api("/groups/#{group.id}/search", user), scope: 'users', search: 'billy'
+          get api("/groups/#{group.id}/search", user), params: { scope: 'users', search: 'billy' }
         end
 
         it_behaves_like 'response is correct', schema: 'public_api/v4/user/basics'
+
+        context 'when users search feature is disabled' do
+          before do
+            allow(Feature).to receive(:disabled?).with(:users_search, default_enabled: true).and_return(true)
+
+            get api("/groups/#{group.id}/search", user), params: { scope: 'users', search: 'billy' }
+          end
+
+          it 'returns 400 error' do
+            expect(response).to have_gitlab_http_status(400)
+          end
+        end
       end
 
       context 'for users scope with group path as id' do
@@ -219,7 +243,7 @@ describe API::Search do
           user1 = create(:user, name: 'billy')
           create(:group_member, :developer, user: user1, group: group)
 
-          get api("/groups/#{CGI.escape(group.full_path)}/search", user), scope: 'users', search: 'billy'
+          get api("/groups/#{CGI.escape(group.full_path)}/search", user), params: { scope: 'users', search: 'billy' }
         end
 
         it_behaves_like 'response is correct', schema: 'public_api/v4/user/basics'
@@ -306,10 +330,22 @@ describe API::Search do
           user1 = create(:user, name: 'billy')
           create(:project_member, :developer, user: user1, project: project)
 
-          get api("/projects/#{project.id}/search", user), scope: 'users', search: 'billy'
+          get api("/projects/#{project.id}/search", user), params: { scope: 'users', search: 'billy' }
         end
 
         it_behaves_like 'response is correct', schema: 'public_api/v4/user/basics'
+
+        context 'when users search feature is disabled' do
+          before do
+            allow(Feature).to receive(:disabled?).with(:users_search, default_enabled: true).and_return(true)
+
+            get api("/projects/#{project.id}/search", user), params: { scope: 'users', search: 'billy' }
+          end
+
+          it 'returns 400 error' do
+            expect(response).to have_gitlab_http_status(400)
+          end
+        end
       end
 
       context 'for notes scope' do