diff --git a/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php b/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php
index 16eb59a..03e5487 100644
--- a/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php
@@ -127,7 +127,7 @@ public function process(ContainerBuilder $container) {
           // Validate the interface.
           $handler = $container->getDefinition($id);
           if (!is_subclass_of($handler->getClass(), $interface)) {
-            throw new LogicException("Service '$id' for consumer '$consumer_id' does not implement $interface.");
+            throw new LogicException("Service '$id' for consumer '$consumer_id' does not implement $interface, or its namespace cannot be resolved.");
           }
           $handlers[$id] = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
           // Keep track of other tagged handlers arguments.