diff --git a/collects/web-server/response.ss b/collects/web-server/response.ss
index 66f687b19f..118d958882 100644
--- a/collects/web-server/response.ss
+++ b/collects/web-server/response.ss
@@ -110,63 +110,68 @@
   
   (define DAYS
     #("Sun" "Mon" "Tue" "Wed" "Thu" "Fri" "Sat"))
-    
+  
   ;; **************************************************
   ;; output-response: connection response -> void
   (define (ext:output-response conn resp)
-    (call-with-semaphore (connection-mutex conn)
-                         (lambda ()
-                           (output-response conn resp)
-                           (flush-output (connection-o-port conn)))))
-
+    (if (connection-close? conn)
+        (raise 'output-response "Attempt to output on closed connection.")
+        (with-handlers ([exn? (lambda (exn)
+                                (kill-connection! conn)
+                                (raise exn))])
+          (call-with-semaphore (connection-mutex conn)
+                               (lambda ()
+                                 (output-response conn resp)
+                                 (flush-output (connection-o-port conn)))))))
+  
   (define (output-response conn resp)
-       (cond
-         [(response/full? resp)
-          (output-response/basic
-           conn resp (response/full->size resp)
-           (lambda (o-port)
-             (for-each
-              (lambda (str) (display str o-port))
-              (response/full-body resp))))]
-         [(response/incremental? resp)
-          (output-response/incremental conn resp)]
-         [(and (pair? resp) (bytes? (car resp)))
-          (output-response/basic
-           conn
-           (make-response/basic 200 "Okay" (current-seconds) (car resp) '())
-           (apply + (map
-                     (lambda (c)
-                       (if (string? c)
-                           (string-length c)
-                           (bytes-length c)))
-                     (cdr resp)))
-           (lambda (o-port)
-             (for-each
-              (lambda (str) (display str o-port))
-              (cdr resp))))]
-         [else
-          ;; TODO: make a real exception for this.
-          (with-handlers
-              ([exn:invalid-xexpr?
-                (lambda (exn)
-                  (output-response/method
-                   conn
-                   (xexpr-exn->response exn resp)
-                   'ignored))]
-               [exn? (lambda (exn)
-                       (raise exn))])
-            (let ([str (and (validate-xexpr resp) (xexpr->string resp))])
-              (output-response/basic
-               conn
-               (make-response/basic 200
-                                    "Okay"
-                                    (current-seconds)
-                                    TEXT/HTML-MIME-TYPE
-                                    '())
-               (add1 (string-length str))
-               (lambda (o-port)
-                 (display str o-port)
-                 (newline o-port)))))]))
+    (cond
+      [(response/full? resp)
+       (output-response/basic
+        conn resp (response/full->size resp)
+        (lambda (o-port)
+          (for-each
+           (lambda (str) (display str o-port))
+           (response/full-body resp))))]
+      [(response/incremental? resp)
+       (output-response/incremental conn resp)]
+      [(and (pair? resp) (bytes? (car resp)))
+       (output-response/basic
+        conn
+        (make-response/basic 200 "Okay" (current-seconds) (car resp) '())
+        (apply + (map
+                  (lambda (c)
+                    (if (string? c)
+                        (string-length c)
+                        (bytes-length c)))
+                  (cdr resp)))
+        (lambda (o-port)
+          (for-each
+           (lambda (str) (display str o-port))
+           (cdr resp))))]
+      [else
+       ;; TODO: make a real exception for this.
+       (with-handlers
+           ([exn:invalid-xexpr?
+             (lambda (exn)
+               (output-response/method
+                conn
+                (xexpr-exn->response exn resp)
+                'ignored))]
+            [exn? (lambda (exn)
+                    (raise exn))])
+         (let ([str (and (validate-xexpr resp) (xexpr->string resp))])
+           (output-response/basic
+            conn
+            (make-response/basic 200
+                                 "Okay"
+                                 (current-seconds)
+                                 TEXT/HTML-MIME-TYPE
+                                 '())
+            (add1 (string-length str))
+            (lambda (o-port)
+              (display str o-port)
+              (newline o-port)))))]))
   
   ;; response/full->size: response/full -> number
   ;; compute the size for a response/full
@@ -181,10 +186,15 @@
   ;; **************************************************
   ;; output-file: connection path symbol bytes -> void
   (define (ext:output-file conn file-path method mime-type)
-    (call-with-semaphore (connection-mutex conn)
-                         (lambda ()
-                           (output-file conn file-path method mime-type)
-                           (flush-output (connection-o-port conn)))))
+    (if (connection-close? conn)
+        (raise 'output-response "Attempt to output on closed connection.")
+        (with-handlers ([exn? (lambda (exn)
+                                (kill-connection! conn)
+                                (raise exn))])
+          (call-with-semaphore (connection-mutex conn)
+                               (lambda ()
+                                 (output-file conn file-path method mime-type)
+                                 (flush-output (connection-o-port conn)))))))
   
   (define (output-file conn file-path method mime-type)
     (output-headers conn 200 "Okay"
@@ -202,11 +212,16 @@
   ;; output-response/method: connection response/full symbol -> void
   ;; If it is a head request output headers only, otherwise output as usual
   (define (ext:output-response/method conn resp meth)
-    (call-with-semaphore (connection-mutex conn)
-                         (lambda ()
-                           (output-response/method conn resp meth)
-                           (flush-output (connection-o-port conn)))))
-
+    (if (connection-close? conn)
+        (raise 'output-response "Attempt to output on closed connection.")
+        (with-handlers ([exn? (lambda (exn)
+                                (kill-connection! conn)
+                                (raise exn))])
+          (call-with-semaphore (connection-mutex conn)
+                               (lambda ()
+                                 (output-response/method conn resp meth)
+                                 (flush-output (connection-o-port conn)))))))
+  
   (define (output-response/method conn resp meth)
     (cond
       [(eqv? meth 'head)