diff --git a/os/hal/src/hal_usb.c b/os/hal/src/hal_usb.c
index 028e42152..813c2a597 100644
--- a/os/hal/src/hal_usb.c
+++ b/os/hal/src/hal_usb.c
@@ -417,14 +417,12 @@ void usbDisableEndpointsI(USBDriver *usbp) {
 #if USB_USE_WAIT == TRUE
     /* Signaling the event to threads waiting on endpoints.*/
     if (usbp->epc[i] != NULL) {
-      osalSysLockFromISR();
       if (usbp->epc[i]->in_state != NULL) {
         osalThreadResumeI(&usbp->epc[i]->in_state->thread, MSG_RESET);
       }
       if (usbp->epc[i]->out_state != NULL) {
         osalThreadResumeI(&usbp->epc[i]->out_state->thread, MSG_RESET);
       }
-      osalSysUnlockFromISR();
     }
 #endif
     usbp->epc[i] = NULL;
diff --git a/readme.txt b/readme.txt
index 6914ab199..b1da2e655 100644
--- a/readme.txt
+++ b/readme.txt
@@ -153,6 +153,8 @@
 - RT:  Merged RT4.
 - NIL: Merged NIL2.
 - NIL: Added STM32F7 demo.
+- HAL: Fixed protocol violation in usbDisableEndpointsI() API (bug #811) 
+       (backported to 16.1.7).
 - HAL: Fixed redefined TIM in STM32F030 registry (bug #809) 
        (backported to 16.1.7).
 - HAL: Fixed clock init in STM32F0x port which doesn't take in account