diff --git a/actionpack/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb b/actionpack/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb
index bd6ffbab5d82b..02daccf22dd9a 100644
--- a/actionpack/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb
+++ b/actionpack/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb
@@ -1,7 +1,7 @@
 <h1>
   <%=h @exception.class.to_s %>
   <% if @request.parameters['controller'] %>
-    in <%=h @request.parameters['controller'].humanize %>Controller<% if @request.parameters['action'] %>#<%=h @request.parameters['action'] %><% end %>
+    in <%=h @request.parameters['controller'].classify.pluralize %>Controller<% if @request.parameters['action'] %>#<%=h @request.parameters['action'] %><% end %>
   <% end %>
 </h1>
 <pre><%=h @exception.message %></pre>
diff --git a/actionpack/test/dispatch/show_exceptions_test.rb b/actionpack/test/dispatch/show_exceptions_test.rb
index 4966527f4d00a..46bec4a5a8dbd 100644
--- a/actionpack/test/dispatch/show_exceptions_test.rb
+++ b/actionpack/test/dispatch/show_exceptions_test.rb
@@ -20,6 +20,8 @@ class ShowExceptionsTest < ActionController::IntegrationTest
     case req.path
     when "/not_found"
       raise ActionController::UnknownAction
+    when "/runtime_error"
+      raise RuntimeError
     when "/method_not_allowed"
       raise ActionController::MethodNotAllowed
     when "/not_implemented"
@@ -115,4 +117,18 @@ class ShowExceptionsTest < ActionController::IntegrationTest
     assert_response 500
     assert_match "&quot;foo&quot;=&gt;&quot;[FILTERED]&quot;", body
   end
+
+  test "show the controller name in the diagnostics template when controller name is present" do
+    @app = ProductionApp
+    get("/runtime_error", {}, {
+      'action_dispatch.show_exceptions' => true,
+      'action_dispatch.request.parameters' => {
+        'action' => 'show',
+        'id' => 'unknown',
+        'controller' => 'featured_tiles'
+      }
+    })
+    assert_response 500
+    assert_match(/RuntimeError\n    in FeaturedTilesController/, body)
+  end
 end