Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 149916)
+++ channels/chan_sip.c	(working copy)
@@ -5607,6 +5607,12 @@
 			ast_rtp_setdtmfcompensate(p->rtp, ast_test_flag(&p->flags[1], SIP_PAGE2_RFC2833_COMPENSATE));
 		} else {
 			ast_set_flag(&p->flags[0], SIP_DTMF_INBAND);
+			if (!p->vad) {
+				p->vad = ast_dsp_new();
+				ast_dsp_set_features(p->vad, DSP_FEATURE_DTMF_DETECT);
+				if (global_relaxdtmf)
+					ast_dsp_digitmode(p->vad, DSP_DIGITMODE_DTMF | DSP_DIGITMODE_RELAXDTMF);
+			}
 		}
 	}