diff --git a/app/vmalert/datasource/vm.go b/app/vmalert/datasource/vm.go
index 2210b8e18..31c43e256 100644
--- a/app/vmalert/datasource/vm.go
+++ b/app/vmalert/datasource/vm.go
@@ -62,6 +62,7 @@ func (s *VMStorage) Clone() *VMStorage {
 		queryStep:        s.queryStep,
 		appendTypePrefix: s.appendTypePrefix,
 		dataSourceType:   s.dataSourceType,
+		extraParams:      s.extraParams,
 	}
 }
 
@@ -69,7 +70,16 @@ func (s *VMStorage) Clone() *VMStorage {
 func (s *VMStorage) ApplyParams(params QuerierParams) *VMStorage {
 	s.dataSourceType = toDatasourceType(params.DataSourceType)
 	s.evaluationInterval = params.EvaluationInterval
-	s.extraParams = params.QueryParams
+	if len(params.QueryParams) != 0 {
+		for k, vl := range params.QueryParams {
+			if s.extraParams.Has(k) {
+				s.extraParams.Del(k)
+			}
+			for _, v := range vl {
+				s.extraParams.Add(k, v)
+			}
+		}
+	}
 	s.debug = params.Debug
 	if params.Headers != nil {
 		for key, value := range params.Headers {
diff --git a/app/vmalert/datasource/vm_test.go b/app/vmalert/datasource/vm_test.go
index 3ae1bf173..3df8805c2 100644
--- a/app/vmalert/datasource/vm_test.go
+++ b/app/vmalert/datasource/vm_test.go
@@ -378,6 +378,9 @@ func TestRequestParams(t *testing.T) {
 	}
 	query := "up"
 	timestamp := time.Date(2001, 2, 3, 4, 5, 6, 0, time.UTC)
+	storage := VMStorage{
+		extraParams: url.Values{"round_digits": {"10"}},
+	}
 	testCases := []struct {
 		name       string
 		queryRange bool
@@ -574,6 +577,17 @@ func TestRequestParams(t *testing.T) {
 				checkEqualString(t, exp, r.URL.RawQuery)
 			},
 		},
+		{
+			"custom params overrides the original params",
+			false,
+			storage.Clone().ApplyParams(QuerierParams{
+				QueryParams: url.Values{"round_digits": {"2"}},
+			}),
+			func(t *testing.T, r *http.Request) {
+				exp := fmt.Sprintf("query=%s&round_digits=2&time=%d", query, timestamp.Unix())
+				checkEqualString(t, exp, r.URL.RawQuery)
+			},
+		},
 		{
 			"graphite extra params",
 			false,