diff --git a/lib/Plack/Middleware/ConditionalGET.pm b/lib/Plack/Middleware/ConditionalGET.pm
index 8a9eb5ea5..9bd28f02b 100644
--- a/lib/Plack/Middleware/ConditionalGET.pm
+++ b/lib/Plack/Middleware/ConditionalGET.pm
@@ -12,7 +12,7 @@ sub call {
 
     $self->response_cb($res, sub {
         my $res = shift;
-
+        return unless $res->[0] == 200;
         my $h = Plack::Util::headers($res->[1]);
 
         # check both ETag and If-Modified-Since, and at least one should exist
diff --git a/t/Plack-Middleware/conditionalget.t b/t/Plack-Middleware/conditionalget.t
index 483ebf14a..c0038b79e 100644
--- a/t/Plack-Middleware/conditionalget.t
+++ b/t/Plack-Middleware/conditionalget.t
@@ -20,6 +20,12 @@ my @tests = (
         status => 304,
         headers => [ ETag => $tag ],
     },
+    {
+        app => sub { [ 404, [ 'ETag' => $tag, 'Content-Type' => 'text/plain' ], [ 'Not Found' ] ] },
+        env => { REQUEST_METHOD => "GET", HTTP_IF_NONE_MATCH => $tag },
+        status => 404,
+        headers => [ ETag => $tag, 'Content-Type' => 'text/plain' ],
+    },
     {
         app => sub { [ 200, [ 'Last-Modified' => $date, 'Content-Type' => 'text/plain' ], [ 'OK' ] ] },
         env => { REQUEST_METHOD => "GET", HTTP_IF_MODIFIED_SINCE => $date },
@@ -80,8 +86,3 @@ for my $block (@tests) {
     is $res->[0], $block->{status};
     is_deeply $res->[1], $block->{headers};
 }
-
-
-
-
-