diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 5889972..2486892 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -969,7 +969,7 @@
 
 /* Visible for testing purposes only */
 #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
-int mbedtls_ssl_dtls_replay_check( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_dtls_replay_check( mbedtls_ssl_context const *ssl );
 void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
 #endif