diff --git a/notifier/notifier.go b/notifier/notifier.go
index b896d53a4..e9af00a4c 100644
--- a/notifier/notifier.go
+++ b/notifier/notifier.go
@@ -77,12 +77,18 @@ type Options struct {
 	QueueCapacity  int
 	ExternalLabels model.LabelSet
 	RelabelConfigs []*config.RelabelConfig
+	// Used for sending HTTP requests to the Alertmanager.
+	Do func(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error)
 }
 
 // New constructs a new Notifier.
 func New(o *Options) *Notifier {
 	ctx, cancel := context.WithCancel(context.Background())
 
+	if o.Do == nil {
+		o.Do = ctxhttp.Do
+	}
+
 	return &Notifier{
 		queue:  make(model.Alerts, 0, o.QueueCapacity),
 		ctx:    ctx,
@@ -351,7 +357,12 @@ func (n *Notifier) sendAll(alerts ...*model.Alert) bool {
 }
 
 func (n *Notifier) sendOne(ctx context.Context, c *http.Client, url string, b []byte) error {
-	resp, err := ctxhttp.Post(ctx, c, url, contentTypeJSON, bytes.NewReader(b))
+	req, err := http.NewRequest("POST", url, bytes.NewReader(b))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", contentTypeJSON)
+	resp, err := n.opts.Do(ctx, c, req)
 	if err != nil {
 		return err
 	}
diff --git a/notifier/notifier_test.go b/notifier/notifier_test.go
index 65c49a3fa..3587a1a8a 100644
--- a/notifier/notifier_test.go
+++ b/notifier/notifier_test.go
@@ -16,12 +16,15 @@ package notifier
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
 	"testing"
 	"time"
 
+	"golang.org/x/net/context"
+
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/config"
 )
@@ -191,6 +194,37 @@ func TestHandlerSendAll(t *testing.T) {
 	}
 }
 
+func TestCustomDo(t *testing.T) {
+	const testURL = "http://testurl.com/"
+	const testBody = "testbody"
+
+	var received bool
+	h := New(&Options{
+		Do: func(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
+			received = true
+			body, err := ioutil.ReadAll(req.Body)
+			if err != nil {
+				t.Fatalf("Unable to read request body: %v", err)
+			}
+			if string(body) != testBody {
+				t.Fatalf("Unexpected body; want %v, got %v", testBody, string(body))
+			}
+			if req.URL.String() != testURL {
+				t.Fatalf("Unexpected URL; want %v, got %v", testURL, req.URL.String())
+			}
+			return &http.Response{
+				Body: ioutil.NopCloser(nil),
+			}, nil
+		},
+	})
+
+	h.sendOne(context.Background(), nil, testURL, []byte(testBody))
+
+	if !received {
+		t.Fatal("Expected to receive an alert, but didn't")
+	}
+}
+
 func TestExternalLabels(t *testing.T) {
 	h := New(&Options{
 		QueueCapacity:  3 * maxBatchSize,