diff --git a/includes/class-signature.php b/includes/class-signature.php
index c6036bd..f0ca349 100644
--- a/includes/class-signature.php
+++ b/includes/class-signature.php
@@ -110,7 +110,7 @@ class Signature {
 		}
 	}
 
-	public static function verify_http_signature( $request = null ) {
+	public static function verify_http_signature( $request ) {
 		$headers = $request->get_headers();
 		$actor = isset( json_decode( $request->get_body() )->actor ) ? json_decode( $request->get_body() )->actor : '';
 		$headers['(request-target)'][0] = strtolower( $request->get_method() ) . ' /wp-json' . $request->get_route();