diff --git a/include/grpc++/impl/rpc_service_method.h b/include/grpc++/impl/rpc_service_method.h
index fcb0b7ccce6..9d30d9627cc 100644
--- a/include/grpc++/impl/rpc_service_method.h
+++ b/include/grpc++/impl/rpc_service_method.h
@@ -251,7 +251,11 @@ class RpcService {
   void AddMethod(RpcServiceMethod* method) { methods_.emplace_back(method); }
 
   RpcServiceMethod* GetMethod(int i) { return methods_[i].get(); }
-  int GetMethodCount() const { return methods_.size(); }
+  int GetMethodCount() const {
+    // On win x64, int is only 32bit
+    GPR_ASSERT(methods_.size() <= INT_MAX);
+    return (int)methods_.size();
+  }
 
  private:
   std::vector<std::unique_ptr<RpcServiceMethod>> methods_;
diff --git a/src/cpp/proto/proto_utils.cc b/src/cpp/proto/proto_utils.cc
index b1330fde7f6..0a05f292221 100644
--- a/src/cpp/proto/proto_utils.cc
+++ b/src/cpp/proto/proto_utils.cc
@@ -70,7 +70,9 @@ class GrpcBufferWriter GRPC_FINAL
       slice_ = gpr_slice_malloc(block_size_);
     }
     *data = GPR_SLICE_START_PTR(slice_);
-    byte_count_ += * size = GPR_SLICE_LENGTH(slice_);
+    // On win x64, int is only 32bit
+    GPR_ASSERT(GPR_SLICE_LENGTH(slice_) <= INT_MAX);
+    byte_count_ += * size = (int)GPR_SLICE_LENGTH(slice_);
     gpr_slice_buffer_add(slice_buffer_, slice_);
     return true;
   }
@@ -124,7 +126,9 @@ class GrpcBufferReader GRPC_FINAL
     }
     gpr_slice_unref(slice_);
     *data = GPR_SLICE_START_PTR(slice_);
-    byte_count_ += * size = GPR_SLICE_LENGTH(slice_);
+    // On win x64, int is only 32bit
+    GPR_ASSERT(GPR_SLICE_LENGTH(slice_) <= INT_MAX);
+    byte_count_ += * size = (int)GPR_SLICE_LENGTH(slice_);
     return true;
   }