diff --git a/src/_h5ai/server/php/inc/class-api.php b/src/_h5ai/server/php/inc/class-api.php
index 10c51132..a52d8971 100644
--- a/src/_h5ai/server/php/inc/class-api.php
+++ b/src/_h5ai/server/php/inc/class-api.php
@@ -19,7 +19,7 @@ class Api {
 		$action = use_request_param("action");
 		json_fail(100, "unsupported request", !in_array($action, $this->actions));
 
-		$methodname = "on_$action";
+		$methodname = "on_${action}";
 		$this->$methodname();
 	}