diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index b0dabf2dd..1f878b71f 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -12709,6 +12709,7 @@ void mbedtls_ssl_free( mbedtls_ssl_context *ssl )
 #endif
         mbedtls_platform_zeroize( ssl->out_buf, out_buf_len );
         mbedtls_free( ssl->out_buf );
+        ssl->out_buf = NULL;
     }
 
     if( ssl->in_buf != NULL )
@@ -12720,6 +12721,7 @@ void mbedtls_ssl_free( mbedtls_ssl_context *ssl )
 #endif
         mbedtls_platform_zeroize( ssl->in_buf, in_buf_len );
         mbedtls_free( ssl->in_buf );
+        ssl->in_buf = NULL;
     }
 
 #if defined(MBEDTLS_ZLIB_SUPPORT)