diff --git a/ref/fips202.c b/ref/fips202.c
index d4b50a43..ab3d2a12 100644
--- a/ref/fips202.c
+++ b/ref/fips202.c
@@ -772,17 +772,3 @@ void sha3_512(uint8_t h[64], const uint8_t *in, size_t inlen)
   for(i=0;i<8;i++)
     store64(h+8*i,s[i]);
 }
-
-
-/*
-void sha3_512_init(keccak_state *s) {
-}
-
-void sha3_512_update(keccak_state *s, const uint8_t *in, size_t inlen) {
-  state->pos = keccak_absorb(state->s, state->pos, SHA3_RATE, in, inlen);
-}
-
-void sha3_512_finalize(uint8_t h[64], const keccak_state *s) {
-  state->pos = keccak_squeeze(out, outlen, state->s, state->pos, SHAKE128_RATE);
-}
-*/
diff --git a/ref/symmetric-shake.c b/ref/symmetric-shake.c
index 67633173..6a990719 100644
--- a/ref/symmetric-shake.c
+++ b/ref/symmetric-shake.c
@@ -63,11 +63,11 @@ void kyber_shake256_prf(uint8_t *out, size_t outlen, const uint8_t key[KYBER_SYM
 **************************************************/
 void kyber_shake256_rkprf(uint8_t out[KYBER_SSBYTES], const uint8_t key[KYBER_SYMBYTES], const uint8_t input[KYBER_CIPHERTEXTBYTES])
 {
-  uint8_t buf[KYBER_SYMBYTES+KYBER_CIPHERTEXTBYTES];
+  keccak_state s;
 
-  /* XXX: Instead of memcpy, use incremental API here */
-  memcpy(buf, key, KYBER_SYMBYTES);
-  memcpy(buf+KYBER_SYMBYTES, input, KYBER_CIPHERTEXTBYTES);
-
-  shake256(out, KYBER_SSBYTES, buf, sizeof(buf));
+  shake256_init(&s);
+  shake256_absorb(&s, key, KYBER_SYMBYTES);
+  shake256_absorb(&s, input, KYBER_CIPHERTEXTBYTES);
+  shake256_finalize(&s);
+  shake256_squeeze(out, KYBER_SSBYTES, &s);
 }