diff --git a/src/ca/virtualCircuit.h b/src/ca/virtualCircuit.h
index 28ed5689f..08dcf305e 100644
--- a/src/ca/virtualCircuit.h
+++ b/src/ca/virtualCircuit.h
@@ -174,6 +174,7 @@ private:
     unsigned recvBytes ( void *pBuf, unsigned nBytesInBuf ) epicsThrows (());
     void connect ();
     const char * pHostName () const;
+    void blockUntilBytesArePendingInOS () const;
 
     // send protocol stubs
     void echoRequest ( epicsGuard < cacMutex > & );