diff --git a/src/gprs/gb_proxy.c b/src/gprs/gb_proxy.c
index 3da7bfd..3f471ff 100644
--- a/src/gprs/gb_proxy.c
+++ b/src/gprs/gb_proxy.c
@@ -243,7 +243,7 @@
 				break;
 			}
 
-			bss_ptmsi = bss_ptmsi | 0xC0000000;
+			bss_ptmsi = bss_ptmsi | GSM23003_TMSI_SGSN_MASK;
 
 			if (gbproxy_link_info_by_ptmsi(peer, bss_ptmsi))
 				bss_ptmsi = GSM_RESERVED_TMSI;
diff --git a/src/gprs/gprs_sgsn.c b/src/gprs/gprs_sgsn.c
index 5801107..8d3de7b 100644
--- a/src/gprs/gprs_sgsn.c
+++ b/src/gprs/gprs_sgsn.c
@@ -692,12 +692,12 @@
 	 * Alternatively, a freeze list could be used if another PRNG is used
 	 * or when this approach proves to be not sufficient.
 	 */
-	if (ptmsi >= 0xC0000000) {
+	if (ptmsi >= GSM23003_TMSI_SGSN_MASK) {
 		if (!max_retries--)
 			goto failed;
 		goto restart;
 	}
-	ptmsi |= 0xC0000000;
+	ptmsi |= GSM23003_TMSI_SGSN_MASK;
 
 	if (ptmsi == GSM_RESERVED_TMSI) {
 		if (!max_retries--)