diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 5eaf073..78640d6 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -3518,24 +3518,77 @@
 
   // FIXME: Sync this with InitializePredefinedMacros; we need to match int8_t
   // and friends, at least with glibc.
+  // FIXME: Make sure 32/64-bit integers don't get defined to types of the wrong
+  // width on unusual platforms.
   // FIXME: Make sure floating-point mappings are accurate
   // FIXME: Support XF and TF types
-  if (!DestWidth) {
+  QualType NewTy;
+  switch (DestWidth) {
+  case 0:
     S.Diag(Attr.getLoc(), diag::err_unknown_machine_mode) << Name;
     return;
-  }
-
-  QualType NewTy;
-
-  if (IntegerMode)
-    NewTy = S.Context.getIntTypeForBitwidth(DestWidth,
-                                            OldTy->isSignedIntegerType());
-  else
-    NewTy = S.Context.getRealTypeForBitwidth(DestWidth);
-
-  if (NewTy.isNull()) {
+  default:
     S.Diag(Attr.getLoc(), diag::err_unsupported_machine_mode) << Name;
     return;
+  case 8:
+    if (!IntegerMode) {
+      S.Diag(Attr.getLoc(), diag::err_unsupported_machine_mode) << Name;
+      return;
+    }
+    if (OldTy->isSignedIntegerType())
+      NewTy = S.Context.SignedCharTy;
+    else
+      NewTy = S.Context.UnsignedCharTy;
+    break;
+  case 16:
+    if (!IntegerMode) {
+      S.Diag(Attr.getLoc(), diag::err_unsupported_machine_mode) << Name;
+      return;
+    }
+    if (OldTy->isSignedIntegerType())
+      NewTy = S.Context.ShortTy;
+    else
+      NewTy = S.Context.UnsignedShortTy;
+    break;
+  case 32:
+    if (!IntegerMode)
+      NewTy = S.Context.FloatTy;
+    else if (OldTy->isSignedIntegerType())
+      NewTy = S.Context.IntTy;
+    else
+      NewTy = S.Context.UnsignedIntTy;
+    break;
+  case 64:
+    if (!IntegerMode)
+      NewTy = S.Context.DoubleTy;
+    else if (OldTy->isSignedIntegerType())
+      if (S.Context.getTargetInfo().getLongWidth() == 64)
+        NewTy = S.Context.LongTy;
+      else
+        NewTy = S.Context.LongLongTy;
+    else
+      if (S.Context.getTargetInfo().getLongWidth() == 64)
+        NewTy = S.Context.UnsignedLongTy;
+      else
+        NewTy = S.Context.UnsignedLongLongTy;
+    break;
+  case 96:
+    NewTy = S.Context.LongDoubleTy;
+    break;
+  case 128:
+    if (!IntegerMode && &S.Context.getTargetInfo().getLongDoubleFormat() !=
+        &llvm::APFloat::PPCDoubleDouble) {
+      S.Diag(Attr.getLoc(), diag::err_unsupported_machine_mode) << Name;
+      return;
+    }
+    if (IntegerMode) {
+      if (OldTy->isSignedIntegerType())
+        NewTy = S.Context.Int128Ty;
+      else
+        NewTy = S.Context.UnsignedInt128Ty;
+    } else
+      NewTy = S.Context.LongDoubleTy;
+    break;
   }
 
   if (ComplexMode) {