diff --git a/tommath.h b/tommath.h
index b806c3b..742bb9a 100644
--- a/tommath.h
+++ b/tommath.h
@@ -200,7 +200,7 @@ extern int KARATSUBA_MUL_CUTOFF,
 #endif
 
 /* size of comba arrays, should be at least 2 * 2**(BITS_PER_WORD - BITS_PER_DIGIT*2) */
-#define MP_WARRAY               (1 << ((sizeof(mp_word) * CHAR_BIT) - (2 * DIGIT_BIT) + 1))
+#define MP_WARRAY               (1 << (((sizeof(mp_word) * CHAR_BIT) - (2 * DIGIT_BIT)) + 1))
 
 /* the infamous mp_int structure */
 typedef struct  {