diff --git a/src/bts.cpp b/src/bts.cpp
index bcf4d1b0..4fe529ec 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -1066,7 +1066,7 @@ GprsMs *bts_alloc_ms(struct gprs_rlcmac_bts* bts, uint8_t ms_class, uint8_t egpr
 	return ms;
 }
 
-struct GprsMsStorage *bts_ms_store(struct gprs_rlcmac_bts *bts)
+struct GprsMsStorage *bts_ms_store(const struct gprs_rlcmac_bts *bts)
 {
 	return bts->ms_store;
 }
diff --git a/src/bts.h b/src/bts.h
index a8b4d7b5..ea44fb70 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -301,7 +301,7 @@ void bts_send_gsmtap_rach(struct gprs_rlcmac_bts *bts,
 			  enum pcu_gsmtap_category categ, uint8_t channel,
 			  const struct rach_ind_params *rip);
 
-struct GprsMsStorage *bts_ms_store(struct gprs_rlcmac_bts *bts);
+struct GprsMsStorage *bts_ms_store(const struct gprs_rlcmac_bts *bts);
 
 struct GprsMs *bts_ms_by_tlli(struct gprs_rlcmac_bts *bts, uint32_t tlli, uint32_t old_tlli);