diff --git a/libpri.h b/libpri.h
index fa891d3..74ffe81 100644
--- a/libpri.h
+++ b/libpri.h
@@ -528,9 +528,9 @@ extern int pri_sr_set_caller(struct pri_sr *sr, char *caller, char *callername,
 extern int pri_sr_set_redirecting(struct pri_sr *sr, char *num, int plan, int pres, int reason);
 #define PRI_USER_USER_TX
 /* Set the user user field.  Warning!  don't send binary data accross this field */
-extern void pri_sr_set_useruser(struct pri_sr *sr, char *userchars);
+extern void pri_sr_set_useruser(struct pri_sr *sr, const char *userchars);
 
-extern void pri_call_set_useruser(q931_call *sr, char *userchars);
+extern void pri_call_set_useruser(q931_call *sr, const char *userchars);
 
 extern int pri_setup(struct pri *pri, q931_call *call, struct pri_sr *req);
 
diff --git a/pri.c b/pri.c
index 1cb8069..b56b140 100644
--- a/pri.c
+++ b/pri.c
@@ -247,13 +247,13 @@ static struct pri *__pri_new(int fd, int node, int switchtype, struct pri *maste
 	return p;
 }
 
-void pri_call_set_useruser(q931_call *c, char *userchars)
+void pri_call_set_useruser(q931_call *c, const char *userchars)
 {
 	if (userchars)
 		libpri_copy_string(c->useruserinfo, userchars, sizeof(c->useruserinfo));
 }
 
-void pri_sr_set_useruser(struct pri_sr *sr, char *userchars)
+void pri_sr_set_useruser(struct pri_sr *sr, const char *userchars)
 {
 	sr->useruserinfo = userchars;
 }
diff --git a/pri_internal.h b/pri_internal.h
index a057d92..8912a30 100644
--- a/pri_internal.h
+++ b/pri_internal.h
@@ -129,7 +129,7 @@ struct pri_sr {
 	int redirectingpres;
 	int redirectingreason;
 	int justsignalling;
-	char *useruserinfo;
+	const char *useruserinfo;
 };
 
 /* Internal switch types */