diff --git a/asyn/drvAsynSerial/drvAsynSerialPortWin32.c b/asyn/drvAsynSerial/drvAsynSerialPortWin32.c
index 0562cf5..722ef64 100644
--- a/asyn/drvAsynSerial/drvAsynSerialPortWin32.c
+++ b/asyn/drvAsynSerial/drvAsynSerialPortWin32.c
@@ -183,6 +183,7 @@ static int waitForBytes(ttyController_t *tty, asynUser* pasynUser, double timeou
 		{
 			epicsTimeGetCurrent(&ts);
 			timeout -= epicsTimeDiffInSeconds(&ts, &ts_start);
+			ts_start = ts;
 		}
 		else
 		{