diff --git a/ring-core/src/ring/middleware/not_modified.clj b/ring-core/src/ring/middleware/not_modified.clj
index 99a1d09e..ed2a2bfb 100644
--- a/ring-core/src/ring/middleware/not_modified.clj
+++ b/ring-core/src/ring/middleware/not_modified.clj
@@ -2,7 +2,7 @@
   "Middleware that returns a 304 Not Modified response for responses with
   Last-Modified headers."
   (:require [ring.util.time :refer [parse-date]]
-            [ring.util.response :refer [get-header header]]
+            [ring.util.response :refer [get-header find-header header]]
             [ring.util.io :refer [close!]]))
 
 (defn- etag-match? [request response]
@@ -35,6 +35,11 @@
       (or (not-modified-since? request response)
           (etag-match? request response)))))
 
+(defn- dissoc-header [response header]
+  (if-some [[k _] (find-header response header)]
+    (update response :headers dissoc k)
+    response))
+
 (defn not-modified-response
   "Returns 304 or original response based on response and request.
   See: wrap-not-modified."
@@ -46,7 +51,7 @@
     (do (close! (:body response))
         (-> response
             (assoc :status 304)
-            (header "Content-Length" 0)
+            (dissoc-header "Content-Length")
             (assoc :body nil)))
     response))
 
diff --git a/ring-core/test/ring/middleware/test/not_modified.clj b/ring-core/test/ring/middleware/test/not_modified.clj
index 6e3576c7..2d1e30f6 100644
--- a/ring-core/test/ring/middleware/test/not_modified.clj
+++ b/ring-core/test/ring/middleware/test/not_modified.clj
@@ -71,8 +71,9 @@
           last-modified "Sun, 23 Sep 2012 11:00:00 GMT"
           h-resp {:status 200 :headers {"Last-Modified" last-modified} :body ""}
           resp   (not-modified-response h-resp (req last-modified))]
+      (is (= 304 (:status resp)))
       (is (nil? (:body resp)))
-      (is (= (get-in resp [:headers "Content-Length"]) "0"))))
+      (is (nil? (get-in resp [:headers "Content-Length"])))))
 
   (testing "no modification info"
     (let [response {:status 200 :headers {} :body ""}]
@@ -111,4 +112,16 @@
         200 304
         302 302
         404 404
-        500 500))))
+        500 500)))
+
+  (testing "content-type header is removed"
+    (let [req   #(hash-map :request-method :get :headers {"if-modified-since" %})
+          last-modified "Sun, 23 Sep 2012 11:00:00 GMT"
+          h-resp {:status 200
+                  :headers {"Last-Modified" last-modified
+                            "Content-Length" "11"}
+                  :body "hello world"}
+          resp   (not-modified-response h-resp (req last-modified))]
+      (is (= 304 (:status resp)))
+      (is (nil? (:body resp)))
+      (is (nil? (get-in resp [:headers "Content-Length"]))))))