diff --git a/src/core/util.c b/src/core/util.c
index 636b89a0..8559ceca 100644
--- a/src/core/util.c
+++ b/src/core/util.c
@@ -200,9 +200,9 @@ static uint32_t halfsiphash(const uint8_t *in, const size_t inlen, const uint8_t
 }
 /* end of siphash */
 
-static uint8_t hash_key[16] = {0};
+static uint8_t hash_key[JANET_HASH_KEY_SIZE] = {0};
 
-void janet_init_hash_key(uint8_t new_key[16]) {
+void janet_init_hash_key(uint8_t new_key[JANET_HASH_KEY_SIZE]) {
     memcpy(hash_key, new_key, sizeof(hash_key));
 }
 
diff --git a/src/include/janet.h b/src/include/janet.h
index 0e5931a7..a2120695 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -1303,7 +1303,8 @@ JANET_API JanetBuffer *janet_pretty(JanetBuffer *buffer, int depth, int flags, J
 
 /* Misc */
 #ifndef JANET_NO_PRF
-JANET_API void janet_init_hash_key(uint8_t key[16]);
+#define JANET_HASH_KEY_SIZE 16
+JANET_API void janet_init_hash_key(uint8_t key[JANET_HASH_KEY_SIZE]);
 #endif
 JANET_API int janet_equals(Janet x, Janet y);
 JANET_API int32_t janet_hash(Janet x);