diff --git a/testing/web-platform/tests/webcodecs/image-decoder.any.js b/testing/web-platform/tests/webcodecs/image-decoder.any.js
index f33a60a1f6ca..2c13b72cbd1a 100644
--- a/testing/web-platform/tests/webcodecs/image-decoder.any.js
+++ b/testing/web-platform/tests/webcodecs/image-decoder.any.js
@@ -85,3 +85,18 @@ promise_test(t => {
 promise_test(t => {
   return testFourColorsDecode('four-colors.gif', 'image/gif');
 }, 'Test GIF image decoding.');
+
+promise_test(t => {
+  return fetch('four-colors.png').then(response => {
+    let decoder = new ImageDecoder({data: response.body, type: 'junk/type'});
+    return promise_rejects_dom(t, 'NotSupportedError', decoder.decode());
+  });
+}, 'Test invalid mime type rejects decode() requests');
+
+promise_test(t => {
+  return fetch('four-colors.png').then(response => {
+    let decoder = new ImageDecoder({data: response.body, type: 'junk/type'});
+    return promise_rejects_dom(
+        t, 'NotSupportedError', decoder.decodeMetadata());
+  });
+}, 'Test invalid mime type rejects decodeMetadata() requests');