diff --git a/src/_h5ai/public/index.php b/src/_h5ai/public/index.php
index 9e64788f..f6681f9a 100644
--- a/src/_h5ai/public/index.php
+++ b/src/_h5ai/public/index.php
@@ -8,5 +8,10 @@ if (!function_exists('version_compare') || version_compare(PHP_VERSION, MIN_PHP_
     exit('[ERR] h5ai requires PHP ' . MIN_PHP_VERSION . ' or later, but found PHP ' . PHP_VERSION);
 }
 
+if (substr(H5AI_VERSION, 0, 2) === '{{') {
+    header('Content-type: text/plain;charset=utf-8');
+    exit('[ERR] h5ai sources must be preprocessed to work correctly');
+}
+
 require_once __DIR__ . '/../private/php/class-bootstrap.php';
 Bootstrap::run();