diff --git a/src/openssl/prf.c b/src/openssl/prf.c
index 59e8a3aa..df7f445c 100644
--- a/src/openssl/prf.c
+++ b/src/openssl/prf.c
@@ -71,6 +71,6 @@ bool prf(char *secret, size_t secretlen, char *seed, size_t seedlen, char *out,
 
 	memset(out, 0, outlen);
 
-	return prf_xor(NID_sha512, secret, secretlen / 2, seed, seedlen, out, outlen)
-		&& prf_xor(NID_whirlpool, secret, secretlen / 2, seed, seedlen, out, outlen);
+	return prf_xor(NID_sha512, secret, (secretlen + 1) / 2, seed, seedlen, out, outlen)
+		&& prf_xor(NID_whirlpool, secret + secretlen / 2, (secretlen + 1) / 2, seed, seedlen, out, outlen);
 }