Index: uspace/drv/bus/usb/ehci/hc.c
===================================================================
--- uspace/drv/bus/usb/ehci/hc.c	(revision d97f91fd1b5f5edaa365f6ebdda0d819ac98d561)
+++ uspace/drv/bus/usb/ehci/hc.c	(revision 580b330fe54bf46462dafb17536eca6600a021d0)
@@ -311,6 +311,8 @@
 		ehci_rh_interrupt(&instance->rh);
 	}
-	if (status & USB_STS_ASYNC_SCHED_FLAG) {
+	if (status & USB_STS_IRQ_ASYNC_ADVANCE_FLAG) {
+		fibril_mutex_lock(&instance->guard);
 		fibril_condvar_signal(&instance->async_doorbell);
+		fibril_mutex_unlock(&instance->guard);
 	}
 	if (status & (USB_STS_IRQ_FLAG | USB_STS_ERR_IRQ_FLAG)) {