Index: uspace/lib/usbdev/src/devpoll.c
===================================================================
--- uspace/lib/usbdev/src/devpoll.c	(revision 338729c6d8dfc00f37b27062fff78e556ef22be1)
+++ uspace/lib/usbdev/src/devpoll.c	(revision 4e44f5d3b6bb2bad9ed8e9968525722d93aa5747)
@@ -107,5 +107,8 @@
 	assert(arg);
 	usb_polling_t *polling = arg;
+
+	fibril_mutex_lock(&polling->guard);
 	polling->running = true;
+	fibril_mutex_unlock(&polling->guard);
 
 	usb_pipe_t *pipe = &polling->ep_mapping->pipe;
@@ -208,5 +211,7 @@
 	}
 
+	fibril_mutex_lock(&polling->guard);
 	polling->running = false;
+	fibril_mutex_unlock(&polling->guard);
 
 	/* Notify joiners, if any. */