diff --git a/rules/manager.go b/rules/manager.go
index 993302637..b3ed28f8f 100644
--- a/rules/manager.go
+++ b/rules/manager.go
@@ -163,7 +163,7 @@ func (g *Group) run() {
 		iterationsScheduled.Inc()
 
 		start := time.Now()
-		g.Eval()
+		g.Eval(start)
 
 		iterationDuration.Observe(time.Since(start).Seconds())
 	}
@@ -257,9 +257,8 @@ func typeForRule(r Rule) ruleType {
 // Eval runs a single evaluation cycle in which all rules are evaluated in parallel.
 // In the future a single group will be evaluated sequentially to properly handle
 // rule dependency.
-func (g *Group) Eval() {
+func (g *Group) Eval(ts time.Time) {
 	var (
-		now            = time.Now()
 		wg             sync.WaitGroup
 		mu             sync.Mutex
 		seriesReturned = make(map[string]labels.Labels, len(g.seriesInPreviousEval))
@@ -279,7 +278,7 @@ func (g *Group) Eval() {
 
 			evalTotal.WithLabelValues(rtyp).Inc()
 
-			vector, err := rule.Eval(g.opts.Context, now, g.opts.QueryEngine, g.opts.ExternalURL)
+			vector, err := rule.Eval(g.opts.Context, ts, g.opts.QueryEngine, g.opts.ExternalURL)
 			if err != nil {
 				// Canceled queries are intentional termination of queries. This normally
 				// happens on shutdown and thus we skip logging of any errors here.
@@ -344,7 +343,7 @@ func (g *Group) Eval() {
 	for metric, lset := range g.seriesInPreviousEval {
 		if _, ok := seriesReturned[metric]; !ok {
 			// Series no longer exposed, mark it stale.
-			_, err = app.Add(lset, timestamp.FromTime(now), math.Float64frombits(value.StaleNaN))
+			_, err = app.Add(lset, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
 			switch err {
 			case nil:
 			case storage.ErrOutOfOrderSample, storage.ErrDuplicateSampleForTimestamp:
diff --git a/rules/manager_test.go b/rules/manager_test.go
index 9493996a9..eab4139ee 100644
--- a/rules/manager_test.go
+++ b/rules/manager_test.go
@@ -14,7 +14,10 @@
 package rules
 
 import (
+	"context"
 	"fmt"
+	"math"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
@@ -23,7 +26,10 @@ import (
 
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/timestamp"
+	"github.com/prometheus/prometheus/pkg/value"
 	"github.com/prometheus/prometheus/promql"
+	"github.com/prometheus/prometheus/storage"
+	"github.com/prometheus/prometheus/util/testutil"
 )
 
 func TestAlertingRule(t *testing.T) {
@@ -156,3 +162,96 @@ func annotateWithTime(lines []string, ts time.Time) []string {
 	}
 	return annotatedLines
 }
+
+func TestStaleness(t *testing.T) {
+	storage := testutil.NewStorage(t)
+	defer storage.Close()
+	engine := promql.NewEngine(storage, nil)
+	opts := &ManagerOptions{
+		QueryEngine: engine,
+		Appendable:  storage,
+		Context:     context.Background(),
+	}
+
+	expr, err := promql.ParseExpr("a + 1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	rule := NewRecordingRule("a_plus_one", expr, labels.Labels{})
+	group := NewGroup("default", time.Second, []Rule{rule}, opts)
+
+	// A time series that has two samples and then goes stale.
+	app, _ := storage.Appender()
+	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 0, 1)
+	if err = app.Commit(); err != nil {
+		t.Fatal(err)
+	}
+	app, _ = storage.Appender()
+	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 1000, 2)
+	if err = app.Commit(); err != nil {
+		t.Fatal(err)
+	}
+	app, _ = storage.Appender()
+	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 2000, math.Float64frombits(value.StaleNaN))
+	if err = app.Commit(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Execute 3 times, 1 second apart.
+	group.Eval(time.Unix(0, 0))
+	group.Eval(time.Unix(1, 0))
+	group.Eval(time.Unix(2, 0))
+
+	querier, err := storage.Querier(0, 2000)
+	defer querier.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+	matcher, _ := labels.NewMatcher(labels.MatchEqual, model.MetricNameLabel, "a_plus_one")
+	seriesSet := querier.Select(matcher)
+	samples, err := readSeriesSet(seriesSet)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	metric := labels.FromStrings(model.MetricNameLabel, "a_plus_one").String()
+	metricSample, ok := samples[metric]
+	if !ok {
+		t.Fatalf("Series %s not returned.", metric)
+	}
+	if !value.IsStaleNaN(metricSample[2].V) {
+		t.Fatalf("Appended second sample not as expected. Wanted: stale NaN Got: %x", math.Float64bits(metricSample[2].V))
+	}
+	metricSample[2].V = 42 // reflect.DeepEqual cannot handle NaN.
+
+	want := map[string][]promql.Point{
+		metric: []promql.Point{{0, 2}, {1000, 3}, {2000, 42}},
+	}
+
+	if !reflect.DeepEqual(want, samples) {
+		t.Fatalf("Returned samples not as expected. Wanted: %+v Got: %+v", want, samples)
+	}
+}
+
+// Convert a SeriesSet into a form useable with reflect.DeepEqual.
+func readSeriesSet(ss storage.SeriesSet) (map[string][]promql.Point, error) {
+	result := map[string][]promql.Point{}
+
+	for ss.Next() {
+		series := ss.At()
+
+		points := []promql.Point{}
+		it := series.Iterator()
+		for it.Next() {
+			t, v := it.At()
+			points = append(points, promql.Point{T: t, V: v})
+		}
+
+		name := series.Labels().String()
+		result[name] = points
+		if err := ss.Err(); err != nil {
+			return nil, err
+		}
+	}
+	return result, nil
+}