diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 69ba0db..39a32c8 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2349,7 +2349,7 @@
     return( 0 );
 }
 
-int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context *ssl,
+int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
                              mbedtls_ssl_transform *transform,
                              mbedtls_record *rec )
 {