diff --git a/client/proxmark3.c b/client/proxmark3.c
index ef3d33e82..5cbacc860 100644
--- a/client/proxmark3.c
+++ b/client/proxmark3.c
@@ -26,7 +26,7 @@
 
 static serial_port sp;
 static UsbCommand txcmd;
-static bool txcmd_pending = false;
+volatile static bool txcmd_pending = false;
 
 void SendCommand(UsbCommand *c) {
 #if 0