diff --git a/src/csharp/ext/grpc_csharp_ext.c b/src/csharp/ext/grpc_csharp_ext.c
index 21f8f89a198..b4588009557 100644
--- a/src/csharp/ext/grpc_csharp_ext.c
+++ b/src/csharp/ext/grpc_csharp_ext.c
@@ -1245,7 +1245,9 @@ GPR_EXPORT void* GPR_CALLTYPE grpcsharp_slice_buffer_adjust_tail_space(
 
   if (buffer->count == 0) {
     // when sending messages, C-core requires that there
-    // is at least on slice, even for empty payload.
+    // is at least one slice, even for empty payload.
+    // TODO(jtattermusch): this fix can be removed once
+    // https://github.com/grpc/grpc/issues/21299 is fixed.
     grpc_slice_buffer_add_indexed(buffer, grpc_empty_slice());
   }
   grpc_slice* last_slice = &(buffer->slices[buffer->count - 1]);