diff --git a/lib/binding_web/prefix.js b/lib/binding_web/prefix.js
index de01b78a..382035e1 100644
--- a/lib/binding_web/prefix.js
+++ b/lib/binding_web/prefix.js
@@ -11,5 +11,5 @@ var TreeSitter = function() {
 
     static init(moduleOptions) {
       if (initPromise) return initPromise;
-      Module = { ...Module, ...moduleOptions };
+      Module = Object.assign({ }, Module, moduleOptions);
       return initPromise = new Promise((resolveInitPromise) => {