diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
index 4f1c07b..986b141 100644
--- a/library/ssl_cookie.c
+++ b/library/ssl_cookie.c
@@ -165,10 +165,7 @@
     t = ctx->serial++;
 #endif
 
-    (*p)[0] = MBEDTLS_BYTE_3( t );
-    (*p)[1] = MBEDTLS_BYTE_2( t );
-    (*p)[2] = MBEDTLS_BYTE_1( t );
-    (*p)[3] = MBEDTLS_BYTE_0( t );
+    MBEDTLS_PUT_UINT32_BE(t, *p, 0);
     *p += 4;
 
 #if defined(MBEDTLS_THREADING_C)