diff --git a/knots/web-server.scm b/knots/web-server.scm
index ea53ba2..123763d 100644
--- a/knots/web-server.scm
+++ b/knots/web-server.scm
@@ -95,6 +95,25 @@ KEEP-ALIVE? is true."
         r
         (apply extend-response r additional))))
 
+(define (response-maybe-add-connection-header-value request response)
+  (if (memq 'close (response-connection response))
+      ;; Nothing to do
+      response
+      (let* ((v (request-version request))
+             (add-close-header?
+              (case (car v)
+                ((1)
+                 (case (cdr v)
+                   ((1) (memq 'close (request-connection request)))
+                   ((0) (not (memq 'keep-alive (request-connection request))))))
+                (else #t))))
+        (if add-close-header?
+            (extend-response response 'connection '(close))
+            (if (and (= 1 (car v))
+                     (= 0 (cdr v)))
+                (extend-response response 'connection '(keep-alive))
+                response)))))
+
 ;; -> response body
 (define (sanitize-response request response body)
   "\"Sanitize\" the given response and body, making them appropriate for
@@ -155,19 +174,21 @@ on the procedure being called at any particular time."
             response))))
    (else
     ;; check length; assert type; add other required fields?
-    (values (if (procedure? body)
-                (if (response-content-length response)
-                    response
-                    (extend-response response
-                                     'transfer-encoding
-                                     '((chunked))))
-                (let ((rlen (response-content-length response))
-                      (blen (bytevector-length body)))
-                  (cond
-                   (rlen (if (= rlen blen)
-                             response
-                             (error "bad content-length" rlen blen)))
-                   (else (extend-response response 'content-length blen)))))
+    (values (response-maybe-add-connection-header-value
+             request
+             (if (procedure? body)
+                 (if (response-content-length response)
+                     response
+                     (extend-response response
+                                      'transfer-encoding
+                                      '((chunked))))
+                 (let ((rlen (response-content-length response))
+                       (blen (bytevector-length body)))
+                   (cond
+                    (rlen (if (= rlen blen)
+                              response
+                              (error "bad content-length" rlen blen)))
+                    (else (extend-response response 'content-length blen))))))
             (if (eq? (request-method request) 'HEAD)
                 (raise-exception
                  (make-exception-with-irritants
@@ -183,15 +204,7 @@ on the procedure being called at any particular time."
                       (with-stack-and-prompt (lambda () (proc k))))))
 
 (define (keep-alive? response)
-  (let ((v (response-version response)))
-    (and (or (< (response-code response) 400)
-             (= (response-code response) 404))
-         (case (car v)
-           ((1)
-            (case (cdr v)
-              ((1) (not (memq 'close (response-connection response))))
-              ((0) (memq 'keep-alive (response-connection response)))))
-           (else #f)))))
+  (not (memq 'close (response-connection response))))
 
 (define (default-read-request-exception-handler exn)
   (display "While reading request:\n" (current-error-port))
@@ -246,8 +259,11 @@ on the procedure being called at any particular time."
            (cond
             ((not request)
              ;; Bad request.
-             (values (build-response #:version '(1 . 0) #:code 400
-                                     #:headers '((content-length . 0)))
+             (values (build-response
+                      #:version '(1 . 0)
+                      #:code 400
+                      #:headers '((content-length . 0)
+                                  (connection . (close))))
                      #vu8()))
             (else
              (call-with-escape-continuation