diff --git a/includes/Wpup/Headers.php b/includes/Wpup/Headers.php
index 5f4e736..f5c39bb 100644
--- a/includes/Wpup/Headers.php
+++ b/includes/Wpup/Headers.php
@@ -35,7 +35,7 @@ public static function parse($environment) {
 			$key = strtoupper($key);
 			if ( self::isHeaderName($key) ) {
 				//Remove the "HTTP_" prefix that PHP adds to headers stored in $_SERVER.
-				$key = preg_replace('/^http[_\-]/i', '', $key);
+				$key = preg_replace('/^HTTP[_-]/', '', $key);
 				$results[$key] = $value;
 			}
 		}