diff --git a/pixel.cpp b/pixel.cpp
index 042abd20874add20429d1408142566ce635586fd..0a22494feb11eb2ed5fe212855db93ec92361222 100644
--- a/pixel.cpp
+++ b/pixel.cpp
@@ -18,7 +18,7 @@ void decrypt(int data);
 // void toAscii(char *c);
 
 
-void pixel(char *key,
+void pixel(char key[16],
         ap_int<32> selector,
 		ap_int<32> position1,
 		ap_int<32> position2,