diff --git a/include/hamlib/rig.h b/include/hamlib/rig.h
index ad57c3390..458ef51d2 100644
--- a/include/hamlib/rig.h
+++ b/include/hamlib/rig.h
@@ -137,6 +137,11 @@ typedef struct
     int head;
     int tail;
     int flush;  // flush flag for stop_morse
+#if _PTHREAD_H
+    pthread_mutex_t mutex;
+#else
+    int mutex;
+#endif
 } FIFO_RIG;