diff --git a/src/libvlr/vlr.c b/src/libvlr/vlr.c
index 7de78bf..b0e7f79 100644
--- a/src/libvlr/vlr.c
+++ b/src/libvlr/vlr.c
@@ -79,7 +79,7 @@
 }
 
 /* return static buffer with printable name of VLR subscriber */
-const char *vlr_subscr_name(struct vlr_subscr *vsub)
+const char *vlr_subscr_name(const struct vlr_subscr *vsub)
 {
 	static char buf[32];
 	if (!vsub)
@@ -98,7 +98,7 @@
 	return buf;
 }
 
-const char *vlr_subscr_msisdn_or_name(struct vlr_subscr *vsub)
+const char *vlr_subscr_msisdn_or_name(const struct vlr_subscr *vsub)
 {
 	if (!vsub || !vsub->msisdn[0])
 		return vlr_subscr_name(vsub);