podspec nit fix
diff --git a/gRPC-ProtoRPC.podspec b/gRPC-ProtoRPC.podspec
index fab5343..039f3d4 100644
--- a/gRPC-ProtoRPC.podspec
+++ b/gRPC-ProtoRPC.podspec
@@ -42,6 +42,7 @@
 
   src_dir = 'src/objective-c/ProtoRPC'
 
+  s.default_subspec = 'Main'
 
   s.subspec 'Main' do |ss|
     ss.header_mappings_dir = "#{src_dir}"