diff --git a/library/nist_kw.c b/library/nist_kw.c
index e5d7fcd..1aea0b6 100644
--- a/library/nist_kw.c
+++ b/library/nist_kw.c
@@ -379,7 +379,7 @@
             goto cleanup;
 
         /* Check ICV in "constant-time" */
-        diff = mbedtls_cf_memcmp( NIST_KW_ICV1, A, KW_SEMIBLOCK_LENGTH );
+        diff = mbedtls_ct_memcmp( NIST_KW_ICV1, A, KW_SEMIBLOCK_LENGTH );
 
         if( diff != 0 )
         {
@@ -428,7 +428,7 @@
         }
 
         /* Check ICV in "constant-time" */
-        diff = mbedtls_cf_memcmp( NIST_KW_ICV2, A, KW_SEMIBLOCK_LENGTH / 2 );
+        diff = mbedtls_ct_memcmp( NIST_KW_ICV2, A, KW_SEMIBLOCK_LENGTH / 2 );
 
         if( diff != 0 )
         {