diff --git a/collects/tests/racket/basic.rktl b/collects/tests/racket/basic.rktl
index 70afe27c51..39cfd2d63f 100644
--- a/collects/tests/racket/basic.rktl
+++ b/collects/tests/racket/basic.rktl
@@ -1314,15 +1314,16 @@
 ;; unmatched output to a port:
 (for ([succeed? '(#f #t)])
   (for ([N '(1 100 1000 1023 1024 10000)])
-    (define o (open-output-bytes))
-    (void (regexp-match-positions #rx"y" 
-                                  (string-append
-                                   (make-string N #\x) 
-                                   (if succeed? "y" ""))
-                                  0 
-                                  (+ N (if succeed? 1 0))
-                                  o))
-    (test N bytes-length (get-output-bytes o))))
+    (for ([M (list 0 (quotient N 2))])
+      (define o (open-output-bytes))
+      (void (regexp-match-positions #rx"y" 
+                                    (string-append
+                                     (make-string N #\x) 
+                                     (if succeed? "y" ""))
+                                    M
+                                    (+ N (if succeed? 1 0))
+                                    o))
+    (test (- N M) bytes-length (get-output-bytes o)))))
 
 (arity-test regexp 1 1)
 (arity-test regexp? 1 1)
diff --git a/src/racket/src/regexp.c b/src/racket/src/regexp.c
index 660fa085df..1480a2f5e1 100644
--- a/src/racket/src/regexp.c
+++ b/src/racket/src/regexp.c
@@ -5386,7 +5386,7 @@ static Scheme_Object *gen_compare(char *name, int pos,
 
   if (lazy_string) {
     full_s = lazy_string->s;
-    endset = lazy_string->end;
+    endset = lazy_string->end - lazy_string->start;
   }
 
   if (iport) {