diff --git a/web-animations/interfaces/KeyframeEffect/processing-a-keyframes-argument-001.html b/web-animations/interfaces/KeyframeEffect/processing-a-keyframes-argument-001.html
index 133fd579041792..b88c2537deb5e2 100644
--- a/web-animations/interfaces/KeyframeEffect/processing-a-keyframes-argument-001.html
+++ b/web-animations/interfaces/KeyframeEffect/processing-a-keyframes-argument-001.html
@@ -307,6 +307,20 @@
 }, 'Keyframes are read from a custom iterator with where an offset is'
    + ' specified');
 
+test(() => {
+  const test_error = { name: 'test' };
+  const bad_keyframe = { get left() { throw test_error; } };
+  assert_throws(bad_keyframe, () => {
+    new KeyframeEffect(null, createIteratble([
+      { done: false, value: { left: '100px' } },
+      { done: false, value: bad_keyframe },
+      { done: false, value: { left: '200px' } },
+      { done: true },
+    ]));
+  });
+}, 'If a keyframe throws for an animatable property, that exception should be'
+    + ' propagated');
+
 test(() => {
   assert_throws({ name: 'TypeError' }, () => {
     new KeyframeEffect(null, createIterable([
@@ -319,6 +333,30 @@
 }, 'Reading from a custom iterator that returns a non-object keyframe'
    + ' should throw');
 
+test(() => {
+  assert_throws({ name: 'TypeError' }, () => {
+    new KeyframeEffect(null, createIterable([
+      { done: false, value: { left: '100px' } },
+      { done: false },  // No value member; keyframe is undefined.
+      { done: false, value: { left: '200px' } },
+      { done: true },
+    ]));
+  });
+}, 'Reading from a custom iterator that returns an undefined keyframe'
+   + ' should throw');
+
+test(() => {
+  assert_throws({ name: 'TypeError' }, () => {
+    new KeyframeEffect(null, createIterable([
+      { done: false, value: { left: '100px' } },
+      { done: false, value: null },
+      { done: false, value: { left: '200px' } },
+      { done: true },
+    ]));
+  });
+}, 'Reading from a custom iterator that returns a null keyframe'
+   + ' should throw');
+
 test(() => {
   const effect = new KeyframeEffect(null, createIterable([
     { done: false, value: { left: ['100px', '200px'] } },
@@ -329,6 +367,32 @@
   ]);
 }, 'A list of values returned from a custom iterator should be ignored');
 
+// Test handling of invalid Symbol.iterator
+
+test(() => {
+  const test_error = { name: 'test' };
+  const keyframe_obj = {
+    [Symbol.iterator]() {
+      throw test_error;
+    },
+  };
+  assert_throws(test_error, () => {
+    new KeyframeEffect(null, keyframe_obj);
+  });
+}, 'Accessing a Symbol.iterator property that throws should rethrow');
+
+test(() => {
+  const keyframe_obj = {
+    [Symbol.iterator]() {
+      return 42;  // Not an object.
+    },
+  };
+  assert_throws(new TypeError(), () => {
+    new KeyframeEffect(null, keyframe_obj);
+  });
+}, 'A non-object returned from the Symbol.iterator property should cause a'
+    + ' TypeError to be thrown');
+
 test(() => {
   const keyframe = {};
   Object.defineProperty(keyframe, 'width', { value: '200px' });