diff --git a/libcc1/libcc1plugin.cc b/libcc1/libcc1plugin.cc
index 283eaf20685..34dcd89b1b3 100644
--- a/libcc1/libcc1plugin.cc
+++ b/libcc1/libcc1plugin.cc
@@ -454,6 +454,7 @@ plugin_build_enum_type (cc1_plugin::connection *self,
 
   TYPE_PRECISION (result) = TYPE_PRECISION (underlying_int_type);
   TYPE_UNSIGNED (result) = TYPE_UNSIGNED (underlying_int_type);
+  ENUM_UNDERLYING_TYPE (result) = underlying_int_type;
 
   plugin_context *ctx = static_cast<plugin_context *> (self);
   return convert_out (ctx->preserve (result));