diff --git a/spec.emu b/spec.emu
index 86c45b8..ff68a3f 100644
--- a/spec.emu
+++ b/spec.emu
@@ -15,8 +15,11 @@ copyright: false
   <emu-alg>
     1. Let _O_ be the *this* value.
     1. If _O_ is not an Object, throw a *TypeError* exception.
-    1. If _chunkSize_ is not an integral Number in the inclusive interval from *1*<sub>𝔽</sub> to 𝔽(2<sup>32</sup> - 1), throw a *RangeError* exception.
-    1. Let _iterated_ be ? GetIteratorDirect(_O_).
+    1. Let _iterated_ be the Iterator Record { [[Iterator]]: _O_, [[NextMethod]]: *undefined*, [[Done]]: *false* }.
+    1. If _chunkSize_ is not an integral Number in the inclusive interval from *1*<sub>𝔽</sub> to 𝔽(2<sup>32</sup> - 1), then
+      1. Let _error_ be ThrowCompletion(a newly created *RangeError* object).
+      1. Return ? IteratorClose(_iterated_, _error_).
+    1. Set _iterated_ to ? GetIteratorDirect(_O_).
     1. Let _closure_ be a new Abstract Closure with no parameters that captures _iterated_ and _chunkSize_ and performs the following steps when called:
       1. Let _buffer_ be a new empty List.
       1. Repeat,
@@ -42,8 +45,11 @@ copyright: false
   <emu-alg>
     1. Let _O_ be the *this* value.
     1. If _O_ is not an Object, throw a *TypeError* exception.
-    1. If _windowSize_ is not an integral Number in the inclusive interval from *1*<sub>𝔽</sub> to 𝔽(2<sup>32</sup> - 1), throw a *RangeError* exception.
-    1. Let _iterated_ be ? GetIteratorDirect(_O_).
+    1. Let _iterated_ be the Iterator Record { [[Iterator]]: _O_, [[NextMethod]]: *undefined*, [[Done]]: *false* }.
+    1. If _windowSize_ is not an integral Number in the inclusive interval from *1*<sub>𝔽</sub> to 𝔽(2<sup>32</sup> - 1), then
+      1. Let _error_ be ThrowCompletion(a newly created *RangeError* object).
+      1. Return ? IteratorClose(_iterated_, _error_).
+    1. Set _iterated_ to ? GetIteratorDirect(_O_).
     1. Let _closure_ be a new Abstract Closure with no parameters that captures _iterated_ and _windowSize_ and performs the following steps when called:
       1. Let _buffer_ be a new empty List.
       1. Repeat,