diff --git a/olimex.c b/olimex.c
index acf63d7..46b4da4 100644
--- a/olimex.c
+++ b/olimex.c
@@ -272,7 +272,7 @@ transport_t olimex_open(const char *devpath, const char *requested_serial)
 	/* Flush out lingering data */
 	while (usb_bulk_read(tr->handle, tr->in_ep,
 			     buf, sizeof(buf),
-			     100) >= 0);
+			     100) > 0);
 
 	return (transport_t)tr;
 }
diff --git a/rf2500.c b/rf2500.c
index c3772e3..05007e4 100644
--- a/rf2500.c
+++ b/rf2500.c
@@ -231,7 +231,7 @@ transport_t rf2500_open(const char *devpath, const char *requested_serial)
 #ifndef __APPLE__
 	while (usb_bulk_read(tr->handle, USB_FET_IN_EP,
 			     buf, sizeof(buf),
-			     100) >= 0);
+			     100) > 0);
 #endif
 
 	return (transport_t)tr;