diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 68b32a3..93a7cdc 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -152,11 +152,8 @@
      *     (Total is padded to a multiple of 16-bytes with zeroes)
      */
     p = buf + MBEDTLS_CTR_DRBG_BLOCKSIZE;
-    *p++ = MBEDTLS_BYTE_3( data_len );
-    *p++ = MBEDTLS_BYTE_2( data_len );
-    *p++ = MBEDTLS_BYTE_1( data_len );
-    *p++ = MBEDTLS_BYTE_0( data_len );
-    p += 3;
+    MBEDTLS_PUT_UINT32_BE( data_len, p, 0);
+    p += 4 + 3;
     *p++ = MBEDTLS_CTR_DRBG_SEEDLEN;
     memcpy( p, data, data_len );
     p[data_len] = 0x80;