diff --git a/drivers/isdn/mISDN/dsp_cmx.c b/drivers/isdn/mISDN/dsp_cmx.c
index e92b1ba4b45e..c2f51cc50760 100644
--- a/drivers/isdn/mISDN/dsp_cmx.c
+++ b/drivers/isdn/mISDN/dsp_cmx.c
@@ -452,10 +452,10 @@ one_member:
 			if (finddsp->features.pcm_id == dsp->features.pcm_id) {
 				if (finddsp->pcm_slot_rx >= 0 &&
 				    finddsp->pcm_slot_rx < sizeof(freeslots))
-					freeslots[finddsp->pcm_slot_tx] = 0;
+					freeslots[finddsp->pcm_slot_rx] = 0;
 				if (finddsp->pcm_slot_tx >= 0 &&
 				    finddsp->pcm_slot_tx < sizeof(freeslots))
-					freeslots[finddsp->pcm_slot_rx] = 0;
+					freeslots[finddsp->pcm_slot_tx] = 0;
 			}
 		}
 		i = 0;