diff --git a/src/IFramePageController.php b/src/IFramePageController.php
index 6a5ea22..aa072a5 100644
--- a/src/IFramePageController.php
+++ b/src/IFramePageController.php
@@ -15,7 +15,7 @@ class IFramePageController extends PageController
         $desiredProtocol = $this->ForceProtocol;
         if ($desiredProtocol && $currentProtocol !== $desiredProtocol) {
             $enforcedLocation = preg_replace(
-                "#^${currentProtocol}#",
+                "#^{$currentProtocol}#",
                 $desiredProtocol ?? '',
                 $this->AbsoluteLink() ?? ''
             );