diff --git a/luprex/cpp/core/lpxserver.cpp b/luprex/cpp/core/lpxserver.cpp
index 4e925ef3..ff2b6906 100644
--- a/luprex/cpp/core/lpxserver.cpp
+++ b/luprex/cpp/core/lpxserver.cpp
@@ -228,6 +228,9 @@ public:
         // If the clock has advanced far enough, tick the master model.
         if (clock >= next_tick_) {
             master_->invoke(Invocation(Invocation::KIND_TICK, 0, 0, ""));
+            for (UniqueClient &client : clients_) {
+                client->async_diff_ = true;
+            }
             next_tick_ += 1.0;
             if (next_tick_ < clock + 0.3) next_tick_ = clock + 0.3;
         }