diff --git a/lib/Cake/Controller/Controller.php b/lib/Cake/Controller/Controller.php
index 8cd10fdf134..78381e90acd 100644
--- a/lib/Cake/Controller/Controller.php
+++ b/lib/Cake/Controller/Controller.php
@@ -514,12 +514,12 @@ protected function _isPrivateAction(ReflectionMethod $method, CakeRequest $reque
 			!$method->isPublic() ||
 			!in_array($method->name, $this->methods)
 		);
-		$prefixes = Router::prefixes();
+		$prefixes = array_map('strtolower', Router::prefixes());
 
 		if (!$privateAction && !empty($prefixes)) {
 			if (empty($request->params['prefix']) && strpos($request->params['action'], '_') > 0) {
 				list($prefix) = explode('_', $request->params['action']);
-				$privateAction = in_array($prefix, $prefixes);
+				$privateAction = in_array(strtolower($prefix), $prefixes);
 			}
 		}
 		return $privateAction;
diff --git a/lib/Cake/Test/Case/Controller/ControllerTest.php b/lib/Cake/Test/Case/Controller/ControllerTest.php
index 534825e3773..f319bd1672d 100644
--- a/lib/Cake/Test/Case/Controller/ControllerTest.php
+++ b/lib/Cake/Test/Case/Controller/ControllerTest.php
@@ -1447,6 +1447,25 @@ public function testInvokeActionPrefixProtection() {
 		$Controller->invokeAction($url);
 	}
 
+/**
+ * test invoking controller methods.
+ *
+ * @expectedException PrivateActionException
+ * @expectedExceptionMessage Private Action TestController::Admin_add() is not directly accessible.
+ * @return void
+ */
+	public function testInvokeActionPrefixProtectionCasing() {
+		Router::reload();
+		Router::connect('/admin/:controller/:action/*', array('prefix' => 'admin'));
+
+		$url = new CakeRequest('test/Admin_add/');
+		$url->addParams(array('controller' => 'test_controller', 'action' => 'Admin_add'));
+		$response = $this->getMock('CakeResponse');
+
+		$Controller = new TestController($url, $response);
+		$Controller->invokeAction($url);
+	}
+
 /**
  * test invoking controller methods.
  *