Add some const
diff --git a/include/grpc++/impl/codegen/call.h b/include/grpc++/impl/codegen/call.h
index fab85d1..a9a5eb9 100644
--- a/include/grpc++/impl/codegen/call.h
+++ b/include/grpc++/impl/codegen/call.h
@@ -656,10 +656,10 @@
     call_hook_->PerformOpsOnCall(ops, this);
   }
 
-  grpc_call* call() { return call_; }
-  CompletionQueue* cq() { return cq_; }
+  grpc_call* call() const { return call_; }
+  CompletionQueue* cq() const { return cq_; }
 
-  int max_message_size() { return max_message_size_; }
+  int max_message_size() const { return max_message_size_; }
 
  private:
   CallHook* call_hook_;