diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 54733d8..6315339 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -2023,8 +2023,10 @@
                                                           CastRange);
 
   UnaryExprOrTypeTrait ExprKind = UETT_SizeOf;
-  if (OpTok.isOneOf(tok::kw_alignof, tok::kw___alignof, tok::kw__Alignof))
+  if (OpTok.isOneOf(tok::kw_alignof, tok::kw__Alignof))
     ExprKind = UETT_AlignOf;
+  else if (OpTok.is(tok::kw___alignof))
+    ExprKind = UETT_PreferredAlignOf;
   else if (OpTok.is(tok::kw_vec_step))
     ExprKind = UETT_VecStep;
   else if (OpTok.is(tok::kw___builtin_omp_required_simd_align))