diff --git a/spec.emu b/spec.emu
index cc1cfb5..c42bf43 100644
--- a/spec.emu
+++ b/spec.emu
@@ -14,14 +14,19 @@ copyright: false
   <emu-alg>
     1. Let _O_ be the *this* value.
     1. If _O_ is not an Object, throw a *TypeError* exception.
+    1. Let _iterated_ be the Iterator Record { [[Iterator]]: _O_, [[NextMethod]]: *undefined*, [[Done]]: *false* }.
     1. If _skippedElements_ is *undefined*, then
       1. Let _toSkip_ be 0.
     1. Else,
-      1. If _skippedElements_ is not one of *+∞<sub>𝔽</sub>*, *-∞<sub>𝔽</sub>*, or an integral Number, throw a *TypeError* exception.
+      1. If _skippedElements_ is not one of *+∞<sub>𝔽</sub>*, *-∞<sub>𝔽</sub>*, or an integral Number, then
+        1. Let _error_ be ThrowCompletion(a newly created *TypeError* object).
+        1. Return ? IteratorClose(_iterated_, _error_).
       1. Let _toSkip_ be the extended mathematical value of _skippedElements_.
-    1. If _toSkip_ &lt; 0, throw a *RangeError* exception.
+    1. If _toSkip_ &lt; 0, then
+      1. Let _error_ be ThrowCompletion(a newly created *RangeError* object).
+      1. Return ? IteratorClose(_iterated_, _error_).
     1. Let _skipped_ be 0.
-    1. Let _iterated_ be ? GetIteratorDirect(_O_).
+    1. Set _iterated_ to ? GetIteratorDirect(_O_).
     1. Repeat,
       1. Let _value_ be ? IteratorStepValue(_iterated_).
       1. If _value_ is ~done~, return *false*.
diff --git a/src/index.ts b/src/index.ts
index 4a7e4d2..996d6c7 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,20 +2,27 @@ function includes<T>(this: IterableIterator<T>, searchElement: T, skippedElement
   let toSkip = 0;
   if (skippedElements !== undefined) {
     if (!(skippedElements === 2e308 || skippedElements === -2e308 || typeof skippedElements === 'number' && Math.trunc(skippedElements) === skippedElements)) {
+      try { this.return?.(); } catch {}
       throw new TypeError;
     }
     toSkip = skippedElements as number;
   }
   if (toSkip < 0) {
+    try { this.return?.(); } catch {}
     throw new RangeError;
   }
   let skipped = 0;
-  for (let e of this) {
+  let next = (Date.bind<typeof this.next>).call(this.next, this);
+  let iteratorResult = next();
+  while (!iteratorResult.done) {
+    let e = iteratorResult.value;
     if (skipped < toSkip) {
       ++skipped;
     } else if ([e].includes(searchElement)) {
+      try { this.return?.(); } catch {}
       return true;
     }
+    iteratorResult = next();
   }
   return false;
 }
diff --git a/test/index.mjs b/test/index.mjs
index 733f654..a21372d 100644
--- a/test/index.mjs
+++ b/test/index.mjs
@@ -56,7 +56,7 @@ test('zeroes', async t => {
   assert.equal(negative.values().includes(-0), true);
 });
 
-test('closes iterator', async t => {
+test('closes iterator after succeeding', async t => {
   let closed = false;
   let i = 0;
   let iter = {
@@ -67,7 +67,7 @@ test('closes iterator', async t => {
     },
     return() {
       closed = true;
-      return { value: undefined, done: true };
+      throw new Error;
     },
   };
 
@@ -75,6 +75,50 @@ test('closes iterator', async t => {
   assert.equal(closed, true);
 });
 
+test('closes iterator after invalid second parameter', async t => {
+  {
+    let closed = false;
+    let i = 0;
+    let iter = {
+      __proto__: Iterator.prototype,
+      next() {
+        ++i;
+        return { value: i, done: false };
+      },
+      return() {
+        closed = true;
+        throw new Error;
+      },
+    };
+
+    assert.throws(() => {
+      iter.includes(null, -2);
+    }, RangeError);
+    assert.equal(closed, true);
+  }
+
+  {
+    let closed = false;
+    let i = 0;
+    let iter = {
+      __proto__: Iterator.prototype,
+      next() {
+        ++i;
+        return { value: i, done: false };
+      },
+      return() {
+        closed = true;
+        throw new Error;
+      },
+    };
+
+    assert.throws(() => {
+      iter.includes(null, 'a string');
+    }, TypeError);
+    assert.equal(closed, true);
+  }
+});
+
 test('skipped elements', async t => {
   await test('negative integral', async t => {
     assert.throws(() => {