diff --git a/sort.c b/sort.c
index 9706e8f..dfc383f 100644
--- a/sort.c
+++ b/sort.c
@@ -68,8 +68,8 @@ skipcolumn(struct line *a, int skip_to_next_col)
 		if ((s = memmem(a->data, a->len, fieldsep, fieldseplen))) {
 			if (skip_to_next_col) {
 				s += fieldseplen;
+				a->len -= s - a->data;
 				a->data = s;
-				a->len = a->len - (s - a->data);
 			}
 		} else {
 			a->data += a->len - 1;