diff --git a/src/gprs_bssgp_pcu.cpp b/src/gprs_bssgp_pcu.cpp
index 802ca9a..dcb1b5b 100644
--- a/src/gprs_bssgp_pcu.cpp
+++ b/src/gprs_bssgp_pcu.cpp
@@ -804,8 +804,8 @@
 	return the_pcu.bctx;
 }
 
-void gprs_bssgp_update_queue_delay(struct timeval *tv_recv,
-	struct timeval *tv_now)
+void gprs_bssgp_update_queue_delay(const struct timeval *tv_recv,
+	const struct timeval *tv_now)
 {
 	struct timeval *delay_sum = &the_pcu.queue_delay_sum;
 	struct timeval tv_delay;
diff --git a/src/gprs_bssgp_pcu.h b/src/gprs_bssgp_pcu.h
index 32be765..112a888 100644
--- a/src/gprs_bssgp_pcu.h
+++ b/src/gprs_bssgp_pcu.h
@@ -83,7 +83,7 @@
 
 struct bssgp_bvc_ctx *gprs_bssgp_pcu_current_bctx(void);
 
-void gprs_bssgp_update_queue_delay(struct timeval *tv_recv,
-		struct timeval *tv_now);
+void gprs_bssgp_update_queue_delay(const struct timeval *tv_recv,
+		const struct timeval *tv_now);
 
 #endif // GPRS_BSSGP_PCU_H
diff --git a/src/llc.cpp b/src/llc.cpp
index 3388db1..8930d2c 100644
--- a/src/llc.cpp
+++ b/src/llc.cpp
@@ -175,7 +175,8 @@
 	timeradd(&now, &csec, tv);
 }
 
-bool gprs_llc_queue::is_frame_expired(struct timeval *tv_now, struct timeval *tv)
+bool gprs_llc_queue::is_frame_expired(const struct timeval *tv_now,
+	const struct timeval *tv)
 {
 	/* Timeout is infinite */
 	if (tv->tv_sec == 0 && tv->tv_usec == 0)
diff --git a/src/llc.h b/src/llc.h
index bd71773..065589d 100644
--- a/src/llc.h
+++ b/src/llc.h
@@ -63,8 +63,10 @@
  * I store the LLC frames that come from the SGSN.
  */
 struct gprs_llc_queue {
-	static void calc_pdu_lifetime(BTS *bts, const uint16_t pdu_delay_csec, struct timeval *tv);
-	static bool is_frame_expired(struct timeval *now, struct timeval *tv);
+	static void calc_pdu_lifetime(BTS *bts, const uint16_t pdu_delay_csec,
+		struct timeval *tv);
+	static bool is_frame_expired(const struct timeval *now,
+		const struct timeval *tv);
 	static bool is_user_data_frame(uint8_t *data, size_t len);
 
 	void init();