diff --git a/index.js b/index.js
index 4e771ee..e591e66 100644
--- a/index.js
+++ b/index.js
@@ -339,6 +339,14 @@ class WorkerHelper {
     });
     this._worker.onmessage = (e) => {
       const {id, data} = e.data;
+      if (data == "messageerror") {
+        this._bad = true;
+        // resolve all existing promises
+        this._promisesByIdMap.forEach(({resolve}) => {
+          resolve({});
+        });
+        return;
+      }
       this._messagesByIdMap.set(id, data);
       this._process(id);
     };
@@ -440,21 +448,13 @@ async function checkWorkers(workerType) {
     }
   }
 
-  addSupportsRow('requestAnimationFrame', rAF);
+  if (workerType === "dedicated") {
+    addSupportsRow('requestAnimationFrame', rAF);
+  }
   addSupportsRow('transferControlToOffscreen', offscreen);
   addSupportsRow('OffscreenCanvas', offscreenSupported);
   addSupportsRow('CanvasRenderingContext2D', twoD);
 
-  let moduleSupport = false;
-  try {
-    const workerModule = new WorkerHelper('worker-module.js');
-    const data = await workerModule.getMessage('ping');
-    moduleSupport = true;
-  } catch (e) {
-    //
-  }
-  addSupportsRow('es6 modules', moduleSupport);
-
   addElemToDocument(el('table', { className: 'worker' }, [
     el('tbody', {}, mapLikeToTableRows(obj, false)),
   ]));
diff --git a/worker-import.js b/worker-import.js
deleted file mode 100644
index 55a033d..0000000
--- a/worker-import.js
+++ /dev/null
@@ -1,3 +0,0 @@
-const msg = "imported";
-
-export default msg;
\ No newline at end of file
diff --git a/worker-module.js b/worker-module.js
deleted file mode 100644
index 4dd6fc3..0000000
--- a/worker-module.js
+++ /dev/null
@@ -1,16 +0,0 @@
-import msg from './worker-import.js';
-
-const handlers = {
-  ping(id) {
-    postMessage({id, data: {msg}});
-  },
-};
-
-self.onmessage = function(e) {
-  const {command, id, data} = e.data;
-  const handler = handlers[command];
-  if (!handler) {
-    throw new Error(`unknown command: ${command}`);
-  }
-  handler(id, data);
-};
\ No newline at end of file
diff --git a/worker.js b/worker.js
index d205446..d1d6577 100644
--- a/worker.js
+++ b/worker.js
@@ -62,4 +62,7 @@ self.onconnect = function(e) {
   port.onmessage = function(event) {
     handleMessage.call(port, event);
   };
+  port.onmessageerror = function() {
+    port.postMessage({data: 'messageerror'});
+  };
 };