diff --git a/library/aes.c b/library/aes.c
index b2e346e..aff0a99 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -397,7 +397,7 @@
  */
 #define ROTL8(x) ( ( (x) << 8 ) & 0xFFFFFFFF ) | ( (x) >> 24 )
 #define XTIME(x) ( ( (x) << 1 ) ^ ( ( (x) & 0x80 ) ? 0x1B : 0x00 ) )
-#define MUL(x,y) ( ( (x) && (y) ) ? pow[(log[x]+log[y]) % 255] : 0 )
+#define MUL(x,y) ( ( (x) && (y) ) ? pow[(log[(x)]+log[(y)]) % 255] : 0 )
 
 static int aes_init_done = 0;