diff --git a/js/call-with-42.wasm b/js/call-with-42.wasm
new file mode 100644
index 0000000..a2e9ad6
Binary files /dev/null and b/js/call-with-42.wasm differ
diff --git a/js/wasm.js b/js/wasm.js
index 38db7d7..dbb3d9d 100644
--- a/js/wasm.js
+++ b/js/wasm.js
@@ -1,6 +1,6 @@
-window.addEventListener("load", () => {
+window.addEventListener("load", async () => {
   let container = h("div", { class: "container" });
-  const supported = (() => {
+  const supported = await (async () => {
     // thanks to https://stackoverflow.com/a/47880734 for this check
     try {
       if (
@@ -10,10 +10,32 @@ window.addEventListener("load", () => {
         const module = new WebAssembly.Module(
           Uint8Array.of(0x0, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00)
         );
-        if (module instanceof WebAssembly.Module)
-          return (
-            new WebAssembly.Instance(module) instanceof WebAssembly.Instance
-          );
+        if (!(module instanceof WebAssembly.Module)) {
+          return false;
+        }
+        if (!(new WebAssembly.Instance(module) instanceof WebAssembly.Instance)) {
+          return false;
+        }
+
+        let wasmFileWorks = false;
+        // Example from https://developer.mozilla.org/en-US/docs/WebAssembly/Using_the_JavaScript_API
+        const importObject = {
+          imports: {
+            imported_func: (arg) => {
+              wasmFileWorks = arg === 42;
+            },
+          },
+        };
+        const obj = await WebAssembly.instantiateStreaming(
+          fetch("/js/call-with-42.wasm"),
+          importObject
+        );
+        obj.instance.exports.exported_func();
+        if (!wasmFileWorks) {
+          return false;
+        }
+
+        return true;
       }
     } catch (e) {}
     return false;