diff --git a/src/mem/packet.hh b/src/mem/packet.hh
index b6a0e7c7d..74a2de135 100644
--- a/src/mem/packet.hh
+++ b/src/mem/packet.hh
@@ -612,6 +612,7 @@ class Packet : public Printable
     void setResponderHadWritable()
     {
         assert(cacheResponding());
+        assert(!responderHadWritable());
         flags.set(RESPONDER_HAD_WRITABLE);
     }
     bool responderHadWritable() const