diff --git a/include/openssl/kyber.h b/include/openssl/kyber.h
index 9f5a3ca..e0268fc 100644
--- a/include/openssl/kyber.h
+++ b/include/openssl/kyber.h
@@ -91,7 +91,7 @@
 // authenticated encryption scheme in order to discover the decapsulation
 // failure.
 OPENSSL_EXPORT void KYBER_decap(
-    uint8_t *out_shared_secret,
+    uint8_t out_shared_secret[KYBER_SHARED_SECRET_BYTES],
     const uint8_t ciphertext[KYBER_CIPHERTEXT_BYTES],
     const struct KYBER_private_key *private_key);