diff --git a/src/tbf.h b/src/tbf.h
index 84c3d394..358a7ad6 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -124,9 +124,9 @@ enum tbf_counters { /* TBF counters from 3GPP TS 44.060 §13.4 */
 
 #define GPRS_RLCMAC_FLAG_CCCH		0 /* assignment on CCCH */
 #define GPRS_RLCMAC_FLAG_PACCH		1 /* assignment on PACCH */
-#define GPRS_RLCMAC_FLAG_DL_ACK		2 /* downlink acknowledge received  */
-#define GPRS_RLCMAC_FLAG_TO_UL_ACK	3
-#define GPRS_RLCMAC_FLAG_TO_DL_ACK	4
+#define GPRS_RLCMAC_FLAG_DL_ACK		2 /* DL TBF: At least one DL ACK/NACK was recieved since it was assigned */
+#define GPRS_RLCMAC_FLAG_TO_UL_ACK	3 /* UL TBF: Failed to receive last polled CTRL ACK confirming our UL ACK/NACK */
+#define GPRS_RLCMAC_FLAG_TO_DL_ACK	4 /* DL TBF: Failed to receive last polled DL ACK/NACK */
 #define GPRS_RLCMAC_FLAG_TO_MASK	0xf0 /* timeout bits */
 
 #define T_START(tbf, t, T, r, f) tbf->t_start(t, T, r, f, __FILE__, __LINE__)