diff --git a/module_usb_audio/clocking.h b/module_usb_audio/clocking.h
index b1b85f57..72237236 100644
--- a/module_usb_audio/clocking.h
+++ b/module_usb_audio/clocking.h
@@ -13,6 +13,6 @@
  *  \param c_clk_int channel connected to the decouple() thread for clock
                      interrupts
  */
-void clockGen (streaming chanend c_spdif_rx, chanend ?c_adat_rx, out port p, chanend c_audio, chanend c_clk_ctl, chanend c_clk_int);
+void clockGen (streaming chanend ?c_spdif_rx, chanend ?c_adat_rx, out port p, chanend c_audio, chanend c_clk_ctl, chanend c_clk_int);
 #endif
 
diff --git a/module_usb_audio/clocking/clockgen.xc b/module_usb_audio/clocking/clockgen.xc
index 4046e328..55808caa 100644
--- a/module_usb_audio/clocking/clockgen.xc
+++ b/module_usb_audio/clocking/clockgen.xc
@@ -200,7 +200,7 @@ extern int samples_to_host_inputs_buff[NUM_USB_CHAN_IN];
 int VendorAudCoreReqs(unsigned cmd, chanend c);
 
 #pragma unsafe arrays
-void clockGen (streaming chanend c_spdif_rx, chanend ?c_adat_rx, out port p, chanend c_dig_rx, chanend c_clk_ctl, chanend c_clk_int)
+void clockGen (streaming chanend ?c_spdif_rx, chanend ?c_adat_rx, out port p, chanend c_dig_rx, chanend c_clk_ctl, chanend c_clk_int)
 {
     timer t_local;
     unsigned timeNextEdge, timeLastEdge, timeNextClockDetection;