diff --git a/collects/mzlib/deflate.rkt b/collects/mzlib/deflate.rkt
index c8d443b504..37b615c4e4 100644
--- a/collects/mzlib/deflate.rkt
+++ b/collects/mzlib/deflate.rkt
@@ -469,7 +469,8 @@
         (longest_match-loop)))
     (define (*++scan)
       (set! scanpos (add1 scanpos))
-      (bytes-ref window-vec scanpos))
+      (and (scanpos . < . window_size) ; the original C code can read past the end of the buffer
+           (bytes-ref window-vec scanpos)))
     (define (*++match)
       (set! matchpos (add1 matchpos))
       (bytes-ref window-vec matchpos))
@@ -479,7 +480,7 @@
                  (eq? (*++scan) (*++match)) (eq? (*++scan) (*++match))
                  (eq? (*++scan) (*++match)) (eq? (*++scan) (*++match))
                  (eq? (*++scan) (*++match)) (eq? (*++scan) (*++match))
-                   (< scanpos strendpos))
+                 (< scanpos strendpos))
         (match-eight)))
 
     (define (longest_match-loop)
diff --git a/collects/tests/file/deflate-me.dat b/collects/tests/file/deflate-me.dat
new file mode 100644
index 0000000000..8d7e374903
Binary files /dev/null and b/collects/tests/file/deflate-me.dat differ
diff --git a/collects/tests/file/gzip.rkt b/collects/tests/file/gzip.rkt
index 3348d2eba5..49047fe043 100644
--- a/collects/tests/file/gzip.rkt
+++ b/collects/tests/file/gzip.rkt
@@ -31,7 +31,15 @@
   (define (rand-bytes)
     (list->bytes (for/list ([j (in-range (random 1000))]) (random 256))))
   (test-big-file)
-  (for ([i (in-range 100)]) (id* (rand-bytes))))
+  (for ([i (in-range 100)]) (id* (rand-bytes)))
+  (regression-test))
+
+(define (regression-test)
+  ;; check for an out-of-range buffer access:
+  (call-with-input-file* 
+   (collection-file-path "deflate-me.dat" "tests/file")
+   (lambda (in)
+     (gzip-through-ports in (open-output-bytes) "defalte-me.dat" (current-seconds)))))
 
 (provide tests)
 (define (tests) (test do (run-tests)))