diff --git a/spec.html b/spec.html
index 404befa9fa..f97696a96a 100644
--- a/spec.html
+++ b/spec.html
@@ -42551,7 +42551,8 @@ <h1>Set.prototype.symmetricDifference ( _other_ )</h1>
             1. Set _next_ to ? IteratorStepValue(_keysIter_).
             1. If _next_ is not ~done~, then
               1. If _next_ is *-0*<sub>𝔽</sub>, set _next_ to *+0*<sub>𝔽</sub>.
-              1. If SetDataIndex(_resultSetData_, _next_) is ~not-found~, let _alreadyInResult_ be *false*. Otherwise let _alreadyInResult_ be *true*.
+              1. Let _resultIndex_ be SetDataIndex(_resultSetData_, _next_).
+              1. If _resultIndex_ is ~not-found~, let _alreadyInResult_ be *false*. Otherwise let _alreadyInResult_ be *true*.
               1. If SetDataHas(_O_.[[SetData]], _next_) is *true*, then
                 1. If _alreadyInResult_ is *true*, set _resultSetData_[_resultIndex_] to ~empty~.
               1. Else,