diff --git a/xen/include/crypto/rijndael.h b/xen/include/crypto/rijndael.h
index 69965783c5..4386be5878 100644
--- a/xen/include/crypto/rijndael.h
+++ b/xen/include/crypto/rijndael.h
@@ -52,7 +52,7 @@ void	 rijndael_encrypt(rijndael_ctx *, const unsigned char *, unsigned char *);
 
 int	rijndaelKeySetupEnc(unsigned int [], const unsigned char [], int);
 int	rijndaelKeySetupDec(unsigned int [], const unsigned char [], int);
-void	rijndaelEncrypt(const unsigned int [], int, const unsigned char [],
-	    unsigned char []);
+void	rijndaelEncrypt(const unsigned int [], int, const unsigned char [16],
+	    unsigned char [16]);
 
 #endif /* __RIJNDAEL_H */