diff --git a/PHPCI/Plugin/Util/Factory.php b/PHPCI/Plugin/Util/Factory.php
index 4e6065e6..09cd44cf 100644
--- a/PHPCI/Plugin/Util/Factory.php
+++ b/PHPCI/Plugin/Util/Factory.php
@@ -75,7 +75,7 @@ class Factory {
      * @throws \InvalidArgumentException
      * @internal param mixed $resource
      */
-    public function registerResource(callable $loader,
+    public function registerResource($loader,
                                      $name = null,
                                      $type = null
     )
@@ -86,6 +86,12 @@ class Factory {
             );
         }
 
+        if (!($loader instanceof \Closure)) {
+            throw new \InvalidArgumentException(
+                '$loader is expected to be a function'
+            );
+        }
+
         $resourceID = $this->getInternalID($type, $name);
 
         $this->container[$resourceID] = $loader;