diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 25d7d25..6cb3590 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -3992,7 +3992,7 @@
 
 #if defined(POLARSSL_SSL_SET_CURVES)
         {
-            pk_context *pk = &ssl->session_negotiate->peer_cert->pk;
+            const pk_context *pk = &ssl->session_negotiate->peer_cert->pk;
 
             /* If certificate uses an EC key, make sure the curve is OK */
             if( pk_can_do( pk, POLARSSL_PK_ECKEY ) &&