diff --git a/src/mod/applications/mod_spandsp/mod_spandsp_fax.c b/src/mod/applications/mod_spandsp/mod_spandsp_fax.c
index 8c8d0103c44..b43e2ea0b5a 100644
--- a/src/mod/applications/mod_spandsp/mod_spandsp_fax.c
+++ b/src/mod/applications/mod_spandsp/mod_spandsp_fax.c
@@ -1421,8 +1421,12 @@ static pvt_t *pvt_init(switch_core_session_t *session, mod_spandsp_fax_applicati
 	if ((tmp = switch_channel_get_variable(channel, "fax_ident"))) {
 		char *data = NULL;
 
-		data = strdup(tmp);
-		switch_url_decode(data);
+		if (!strcmp(tmp, "_undef_")) {
+			data = strdup("");
+		} else {
+			data = strdup(tmp);
+			switch_url_decode(data);
+		}
 		pvt->ident = switch_core_session_strdup(session, data);
 
 		switch_safe_free(data);
@@ -1433,8 +1437,12 @@ static pvt_t *pvt_init(switch_core_session_t *session, mod_spandsp_fax_applicati
 	if ((tmp = switch_channel_get_variable(channel, "fax_header"))) {
 		char *data = NULL;
 
-		data = strdup(tmp);
-		switch_url_decode(data);
+		if (!strcmp(tmp, "_undef_")) {
+			data = strdup("");
+		} else {
+			data = strdup(tmp);
+			switch_url_decode(data);
+		}
 		pvt->header = switch_core_session_strdup(session, data);
 
 		switch_safe_free(data);