diff --git a/drivers/isdn/mISDN/dsp.h b/drivers/isdn/mISDN/dsp.h
index 564ea3efd5e..18af86879c0 100644
--- a/drivers/isdn/mISDN/dsp.h
+++ b/drivers/isdn/mISDN/dsp.h
@@ -116,6 +116,7 @@ struct dsp_conf {
 #define ECHOCAN_BUFF_MASK 0x3ff /* -1 */
 
 struct dsp_dtmf {
+	int		enable; /* dtmf is enabled */
 	int		treshold; /* above this is dtmf (square of) */
 	int		software; /* dtmf uses software decoding */
 	int		hardware; /* dtmf uses hardware decoding */
diff --git a/drivers/isdn/mISDN/dsp_core.c b/drivers/isdn/mISDN/dsp_core.c
index c35750647c6..c12cd2f9425 100644
--- a/drivers/isdn/mISDN/dsp_core.c
+++ b/drivers/isdn/mISDN/dsp_core.c
@@ -306,6 +306,7 @@ dsp_control_req(struct dsp *dsp, struct mISDNhead *hh, struct sk_buff *skb)
 					"to %d\n", *((int *)data));
 			dsp->dtmf.treshold = (*(int *)data) * 10000;
 		}
+		dsp->dtmf.enable = 1;
 		/* init goertzel */
 		dsp_dtmf_goertzel_init(dsp);
 
@@ -316,6 +317,7 @@ dsp_control_req(struct dsp *dsp, struct mISDNhead *hh, struct sk_buff *skb)
 	case DTMF_TONE_STOP: /* turn off DTMF */
 		if (dsp_debug & DEBUG_DSP_CORE)
 			printk(KERN_DEBUG "%s: stop dtmf\n", __func__);
+		dsp->dtmf.enable = 0;
 		dsp->dtmf.hardware = 0;
 		dsp->dtmf.software = 0;
 		break;
diff --git a/drivers/isdn/mISDN/dsp_dtmf.c b/drivers/isdn/mISDN/dsp_dtmf.c
index efc371c1f0d..9ae2d33b06f 100644
--- a/drivers/isdn/mISDN/dsp_dtmf.c
+++ b/drivers/isdn/mISDN/dsp_dtmf.c
@@ -51,6 +51,9 @@ void dsp_dtmf_hardware(struct dsp *dsp)
 {
 	int hardware = 1;
 
+	if (!dsp->dtmf.enable)
+		return;
+
 	if (!dsp->features.hfc_dtmf)
 		hardware = 0;