diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index cda06e5f4c9f444cc929b4882f84a8c9f87d0be0..c61a5dac18c5d39f3d6711620aaeb28b411d4738 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -1103,6 +1103,7 @@ fFlags = [
 -- These -X<blah> flags can all be reversed with -Xno-<blah>
 xFlags :: [(String, DynFlag)]
 xFlags = [
+  ( "CPP",                              Opt_Cpp ),
   ( "PatternGuards",                    Opt_PatternGuards ),
   ( "MagicHash",                        Opt_MagicHash ),
   ( "KindSignatures",                   Opt_KindSignatures ),