diff --git a/index.bs b/index.bs
index b530f8f4..e588c43c 100644
--- a/index.bs
+++ b/index.bs
@@ -9435,7 +9435,7 @@ a reference to the same object that the IDL value represents.
 
     1.  Let |jsArrayBuffer| be the result of [=converted to a JavaScript value|converting=]
         |arrayBuffer| to a JavaScript value.
-    1.  If [$IsDetachedBuffer$](|jsArrayBuffer|) is false, then [=JavaScript/throw=] a
+    1.  If [$IsDetachedBuffer$](|jsArrayBuffer|) is true, then [=JavaScript/throw=] a
         <l spec=ecmascript>{{TypeError}}</l>.
     1.  Let |arrayBufferData| be |jsArrayBuffer|.\[[ArrayBufferData]].
     1.  Let |arrayBufferByteLength| be |jsArrayBuffer|.\[[ArrayBufferByteLength]].