diff --git a/include/osmocom/hnbap/hnbap_common.h b/include/osmocom/hnbap/hnbap_common.h
index af619e27..75981d94 100644
--- a/include/osmocom/hnbap/hnbap_common.h
+++ b/include/osmocom/hnbap/hnbap_common.h
@@ -149,6 +149,6 @@ struct msgb *hnbap_generate_unsuccessful_outcome(
 HNBAP_IE_t *hnbap_new_ie(HNBAP_ProtocolIE_ID_t id, HNBAP_Criticality_t criticality,
 		  asn_TYPE_descriptor_t *type, void *sptr);
 
-char *hnbap_cause_str(HNBAP_Cause_t *cause);
+char *hnbap_cause_str(const HNBAP_Cause_t *cause);
 
 void hnbap_set_log_area(int log_area);
diff --git a/include/osmocom/rua/rua_common.h b/include/osmocom/rua/rua_common.h
index 7967c91b..a88c9a24 100644
--- a/include/osmocom/rua/rua_common.h
+++ b/include/osmocom/rua/rua_common.h
@@ -69,6 +69,6 @@ struct msgb *rua_generate_unsuccessful_outcome(
 RUA_IE_t *rua_new_ie(RUA_ProtocolIE_ID_t id, RUA_Criticality_t criticality,
 		     asn_TYPE_descriptor_t *type, void *sptr);
 
-char *rua_cause_str(RUA_Cause_t *cause);
+char *rua_cause_str(const RUA_Cause_t *cause);
 
 void rua_set_log_area(int log_area);
diff --git a/src/hnbap_common.c b/src/hnbap_common.c
index 67cc30c3..10a29fae 100644
--- a/src/hnbap_common.c
+++ b/src/hnbap_common.c
@@ -78,7 +78,7 @@ static const struct value_string hnbap_cause_misc_vals[] = {
 	{ 0, NULL }
 };
 
-char *hnbap_cause_str(HNBAP_Cause_t *cause)
+char *hnbap_cause_str(const HNBAP_Cause_t *cause)
 {
 	static char buf[32];
 
diff --git a/src/rua_common.c b/src/rua_common.c
index 37cf3bac..0cb84268 100644
--- a/src/rua_common.c
+++ b/src/rua_common.c
@@ -67,7 +67,7 @@ static const struct value_string rua_cause_misc_vals[] = {
 	{ 0, NULL }
 };
 
-char *rua_cause_str(RUA_Cause_t *cause)
+char *rua_cause_str(const RUA_Cause_t *cause)
 {
 	static char buf[32];