Return ContainerNotRunning when trying to kill stopped container

container.go

@@ -1187,10 +1187,18 @@ func (c *Client) KillContainer(opts KillContainerOptions) error {
 	path := "/containers/" + opts.ID + "/kill" + "?" + queryString(opts)
 	resp, err := c.do("POST", path, doOptions{context: opts.Context})
 	if err != nil {
-		if e, ok := err.(*Error); ok && e.Status == http.StatusNotFound {
+		e, ok := err.(*Error)
+		if !ok {
+			return err
+		}
+		switch e.Status {
+		case http.StatusNotFound:
 			return &NoSuchContainer{ID: opts.ID}
+		case http.StatusConflict:
+			return &ContainerNotRunning{ID: opts.ID}
+		default:
+			return err
 		}
-		return err
 	}
 	resp.Body.Close()
 	return nil

container_test.go

@@ -1329,6 +1329,18 @@ func TestKillContainerNotFound(t *testing.T) {
 	}
 }
 
+func TestKillContainerNotRunning(t *testing.T) {
+	t.Parallel()
+	id := "abcd1234567890"
+	msg := fmt.Sprintf("Cannot kill container: %[1]s: Container %[1]s is not running", id)
+	client := newTestClient(&FakeRoundTripper{message: msg, status: http.StatusConflict})
+	err := client.KillContainer(KillContainerOptions{ID: id})
+	expected := &ContainerNotRunning{ID: id}
+	if !reflect.DeepEqual(err, expected) {
+		t.Errorf("KillContainer: Wrong error returned. Want %#v. Got %#v.", expected, err)
+	}
+}
+
 func TestRemoveContainer(t *testing.T) {
 	t.Parallel()
 	fakeRT := &FakeRoundTripper{message: "", status: http.StatusOK}