diff --git a/units-impl-wasm.js b/units-impl-wasm.js
index b8f6191..bf562e1 100644
--- a/units-impl-wasm.js
+++ b/units-impl-wasm.js
@@ -4,13 +4,15 @@
   let _do_a_conversion = Module.cwrap("do_a_conversion", "number", [
     "number",
     "number",
+    "number",
   ]);
 
-  async function convert(from, to = "") {
+  async function convert(from, to = "", system="si") {
     let from_c = Module.stringToNewUTF8(from);
     let to_c = Module.stringToNewUTF8(to);
+    let sys_c = Module.stringToNewUTF8(system);
     let lenBefore = globalThis.printBuffer.length;
-    _do_a_conversion(from_c, to === "" ? 0 : to_c);
+    _do_a_conversion(from_c, to === "" ? 0 : to_c, system);
     return globalThis.printBuffer.slice(lenBefore).trim();
   }