diff --git a/src/gsm/gsm0808_utils.c b/src/gsm/gsm0808_utils.c
index d8c275a..efa9305 100644
--- a/src/gsm/gsm0808_utils.c
+++ b/src/gsm/gsm0808_utils.c
@@ -510,7 +510,7 @@
 	case GSM0808_CHAN_DATA:
 		byte = ct->data_rate;
 
-		if (ct->data_transparent)
+		if (!ct->data_transparent)
 			byte |= 0x40; /* Set T/NT */
 
 		if (ct->data_rate_allowed_is_set) {
@@ -580,7 +580,7 @@
 	case GSM0808_CHAN_DATA:
 		byte = *elem;
 		elem++;
-		ct->data_transparent = byte & 0x40; /* T/NT */
+		ct->data_transparent = !(byte & 0x40); /* T/NT */
 		ct->data_rate = byte & 0x3f;
 
 		/* Optional extension for non-transparent service */