diff --git a/library/nist_kw.c b/library/nist_kw.c
index f2fd82e..4ff5e41 100644
--- a/library/nist_kw.c
+++ b/library/nist_kw.c
@@ -421,7 +421,7 @@
          * larger than 8, because of the type wrap around.
          */
         padlen = in_len - KW_SEMIBLOCK_LENGTH - Plen;
-        ret = -mbedtls_ct_uint_if(padlen & ~7, -MBEDTLS_ERR_CIPHER_AUTH_FAILED, -ret);
+        ret = -(int) mbedtls_ct_uint_if(padlen & ~7, -MBEDTLS_ERR_CIPHER_AUTH_FAILED, -ret);
         padlen &= 7;
 
         /* Check padding in "constant-time" */