diff --git a/include/serpent.h b/include/serpent.h
index 31dfacf0d56da8caa075bedfa9f8aa2d024f0592..0cf482a1543d2a5f781d65fd2307e41e7e8c13d2 100644
--- a/include/serpent.h
+++ b/include/serpent.h
@@ -27,7 +27,7 @@ typedef struct {
 
 /* This performs Serpent's key scheduling algorithm. */
 void
-serpent_setup(SERPENT_context *ctx, const UINT8 key[32]);
+serpent_setup(SERPENT_context *ctx, const UINT8 *key);
 
 /*
  * serpent_encrypt()