diff --git a/src/switch_core_io.c b/src/switch_core_io.c
index 69e98e84f5..7589832d59 100644
--- a/src/switch_core_io.c
+++ b/src/switch_core_io.c
@@ -1845,7 +1845,7 @@ SWITCH_DECLARE(switch_status_t) switch_core_session_send_dtmf(switch_core_sessio
 		}
 
 		if ((digits = switch_channel_get_variable_dup(session->channel, "drop_dtmf_masking_digits", SWITCH_FALSE, -1)) && !zstr(digits)) {
-			char *p;
+			const char *p;
 			switch_dtmf_t x_dtmf = { 0, switch_core_default_dtmf_duration(0), DTMF_FLAG_SKIP_PROCESS, 0};
 
 			switch_channel_clear_flag(session->channel, CF_DROP_DTMF);