diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 7f187e2..bb68f2e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1703,7 +1703,7 @@
 }
 
 void ssl_set_ca_chain( ssl_context *ssl, x509_cert *ca_chain,
-                       x509_crl *ca_crl, char *peer_cn )
+                       x509_crl *ca_crl, const char *peer_cn )
 {
     ssl->ca_chain   = ca_chain;
     ssl->ca_crl     = ca_crl;