Fix build
diff --git a/grpc.gemspec b/grpc.gemspec
index 2fcc18f..bbef356 100755
--- a/grpc.gemspec
+++ b/grpc.gemspec
@@ -256,6 +256,7 @@
   s.files += %w( src/core/lib/surface/init.h )
   s.files += %w( src/core/lib/surface/lame_client.h )
   s.files += %w( src/core/lib/surface/server.h )
+  s.files += %w( src/core/lib/surface/validate_metadata.h )
   s.files += %w( src/core/lib/transport/byte_stream.h )
   s.files += %w( src/core/lib/transport/connectivity_state.h )
   s.files += %w( src/core/lib/transport/error_utils.h )