diff --git a/gcc/toplev.c b/gcc/toplev.c
index 287e26b1021a..bb8e48cc3c0d 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -742,6 +742,8 @@ char *lang_options[] =
   "-Wno-traditional",
   "-Wtrigraphs",
   "-Wno-trigraphs",
+  "-Wundef",
+  "-Wno-undef",
   "-Wwrite-strings",
   "-Wno-write-strings",