diff --git a/crypto/ec/ec_mult.c b/crypto/ec/ec_mult.c
index 4dbc931120..16822a73cf 100644
--- a/crypto/ec/ec_mult.c
+++ b/crypto/ec/ec_mult.c
@@ -175,12 +175,13 @@ static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len, B
  *       (thus the boundaries should be increased)
  */
 #define EC_window_bits_for_scalar_size(b) \
-		((b) >= 2000 ? 6 : \
-		 (b) >=  800 ? 5 : \
-		 (b) >=  300 ? 4 : \
-		 (b) >=   70 ? 3 : \
-		 (b) >=   20 ? 2 : \
-		  1)
+		((size_t) \
+		 ((b) >= 2000 ? 6 : \
+		  (b) >=  800 ? 5 : \
+		  (b) >=  300 ? 4 : \
+		  (b) >=   70 ? 3 : \
+		  (b) >=   20 ? 2 : \
+		   1))
 
 /* Compute
  *      \sum scalars[i]*points[i],