diff --git a/src/mod/endpoints/mod_sofia/sofia.c b/src/mod/endpoints/mod_sofia/sofia.c
index 5ae270c367..40753759ef 100644
--- a/src/mod/endpoints/mod_sofia/sofia.c
+++ b/src/mod/endpoints/mod_sofia/sofia.c
@@ -3498,7 +3498,7 @@ void sofia_handle_sip_i_info(nua_t *nua, sofia_profile_t *profile, nua_handle_t
 					int tmp;
 					/* move signal_ptr where we need it (right past Signal=) */
 					signal_ptr = signal_ptr + 7;
-					if (is_dtmf(*signal_ptr)) {
+					if (*strlen && strlen(signal_ptr) == 1 && is_dtmf(*signal_ptr)) {
 						dtmf.digit = *signal_ptr;
 					} else {
 						tmp = atoi(signal_ptr);