diff --git a/os/hal/src/serial_usb.c b/os/hal/src/serial_usb.c
index 23a323356..000d13951 100644
--- a/os/hal/src/serial_usb.c
+++ b/os/hal/src/serial_usb.c
@@ -323,8 +323,9 @@ void sduDataTransmitted(USBDriver *usbp, usbep_t ep) {
     chSysLockFromIsr();
     usbStartTransmitI(usbp, ep);
   }
-  else if (!(usbp->epc[ep]->in_state->txsize &
-            (usbp->epc[ep]->in_maxsize - 1))) {
+  else if ((usbp->epc[ep]->in_state->txsize > 0) &&
+           !(usbp->epc[ep]->in_state->txsize &
+             (usbp->epc[ep]->in_maxsize - 1))) {
     /* Transmit zero sized packet in case the last one has maximum allowed
        size. Otherwise the recipient may expect more data coming soon and
        not return buffered data to app. See section 5.8.3 Bulk Transfer
diff --git a/readme.txt b/readme.txt
index a41f50c19..6f7b6ebd8 100644
--- a/readme.txt
+++ b/readme.txt
@@ -85,6 +85,7 @@
 *****************************************************************************
 
 *** 2.5.2 ***
+- FIX: Fixed deadlock in Serial_USB driver (bug 3605793).
 - FIX: Fixed compile Error OLIMEX_SAM7_EX256/board.c (bug 3605058).
 - FIX: Fixed bug prevents calling adcStartConversionI() within ISR (bug
   3605053)(backported to 2.4.4).