diff --git a/src/add-ons/kernel/busses/usb/ehci.cpp b/src/add-ons/kernel/busses/usb/ehci.cpp
index ede5be33f9..164ddbe87f 100644
--- a/src/add-ons/kernel/busses/usb/ehci.cpp
+++ b/src/add-ons/kernel/busses/usb/ehci.cpp
@@ -435,6 +435,7 @@ EHCI::SubmitTransfer(Transfer *transfer)
 
 	Pipe *pipe = transfer->TransferPipe();
 	if (pipe->Type() & USB_OBJECT_ISO_PIPE) {
+		TRACE_ERROR("isochronous transfers not implemented\n");
 		// ToDo: implement isochronous transfers...
 		return B_ERROR;
 	}
diff --git a/src/add-ons/kernel/busses/usb/ohci.cpp b/src/add-ons/kernel/busses/usb/ohci.cpp
index 16c8c47541..29034c4eae 100644
--- a/src/add-ons/kernel/busses/usb/ohci.cpp
+++ b/src/add-ons/kernel/busses/usb/ohci.cpp
@@ -1245,6 +1245,7 @@ OHCI::_SubmitTransfer(Transfer *transfer)
 status_t
 OHCI::_SubmitIsochronousTransfer(Transfer *transfer)
 {
+	TRACE_ERROR("isochronous transfers not implemented\n");
 	return B_ERROR;
 }