diff --git a/cpp/ql/src/jsf/lib/section_4_21_Operators/AV_Rule_166.qll b/cpp/ql/src/jsf/lib/section_4_21_Operators/AV_Rule_166.qll
index 0e316e86892..b613472c776 100644
--- a/cpp/ql/src/jsf/lib/section_4_21_Operators/AV_Rule_166.qll
+++ b/cpp/ql/src/jsf/lib/section_4_21_Operators/AV_Rule_166.qll
@@ -13,7 +13,7 @@ class SizeofImpureExprOperator extends SizeofExprOperator {
       not e.(OverloadedPointerDereferenceExpr).getExpr().isPure() and
       not exists(OverloadedArrayExpr op | op = e |
         op.getArrayBase().isPure() and
-        op.getArrayOffset().isPure()
+        forall(Expr offset | offset = op.getAnArrayOffset() | offset.isPure())
       )
     )
   }