No need for += when res is 0 anyway
diff --git a/sort.c b/sort.c
index cb6f851..6479461 100644
--- a/sort.c
+++ b/sort.c
@@ -195,8 +195,8 @@
 		} else {
 			if (!(res = memcmp(col1.data, col2.data,
 			                   MIN(col1.len, col2.len)))) {
-				res += col1.data[MIN(col1.len, col2.len)] -
-				       col2.data[MIN(col1.len, col2.len)];
+				res = col1.data[MIN(col1.len, col2.len)] -
+				      col2.data[MIN(col1.len, col2.len)];
 			}
 		}