diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 79c160e..e27fdff 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -1221,7 +1221,7 @@
         }
 
         memcpy( &ssl->cur_out_ctr[2], ssl->in_ctr + 2,
-                MBEDTLS_SSL_COUNTER_LEN - 2 );
+                sizeof( ssl->cur_out_ctr ) - 2 );
 
 #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
         if( mbedtls_ssl_dtls_replay_check( ssl ) != 0 )