diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index b664fb0..d52d9ef 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -152,10 +152,10 @@
      *     (Total is padded to a multiple of 16-bytes with zeroes)
      */
     p = buf + MBEDTLS_CTR_DRBG_BLOCKSIZE;
-    *p++ = ( data_len >> 24 ) & 0xff;
-    *p++ = ( data_len >> 16 ) & 0xff;
-    *p++ = ( data_len >> 8  ) & 0xff;
-    *p++ = ( data_len       ) & 0xff;
+    *p++ = BYTE_3( data_len );
+    *p++ = BYTE_2( data_len );
+    *p++ = BYTE_1( data_len );
+    *p++ = BYTE_0( data_len );
     p += 3;
     *p++ = MBEDTLS_CTR_DRBG_SEEDLEN;
     memcpy( p, data, data_len );