diff --git a/fill/fill_test.go b/fill/fill_test.go
index 40dc6a2..4246aa1 100644
--- a/fill/fill_test.go
+++ b/fill/fill_test.go
@@ -151,8 +151,11 @@ func fetchFromFile(path string) ([]*whisper.TimeSeriesPoint, error) {
 	}
 	defer wsp.Close()
 
+	now := int(time.Now().Unix())
+	fromTime := now - wsp.Retentions()[0].MaxRetention()
+
 	// Parse and fetch data from it
-	ts, err := wsp.Fetch(0, int(time.Now().Unix()))
+	ts, err := wsp.Fetch(fromTime, now)
 	if err != nil {
 		return tsp, err
 	}
@@ -240,6 +243,130 @@ func TestFill(t *testing.T) {
 	fmt.Println()
 }
 
+func whisperCreateDataMany(path string, ts []*whisper.TimeSeriesPoint) error {
+	os.Remove(path) // Don't care if it fails
+	retentions, err := whisper.ParseRetentionDefs("1m:30m,5m:60m,15m:150m")
+	if err != nil {
+		return err
+	}
+	wsp, err := whisper.Create(path, retentions, whisper.Sum, 0)
+	if err != nil {
+		return err
+	}
+	defer wsp.Close()
+
+	// Iterate through the slice so we can support null values
+	wsp.UpdateMany(ts)
+
+	return nil
+}
+
+func whisperCreateNullsManyArchives(path string) ([]*whisper.TimeSeriesPoint, error) {
+	ts := make([]*whisper.TimeSeriesPoint, 150)
+
+	os.Remove(path) // Don't care if it fails
+	retentions, err := whisper.ParseRetentionDefs("1m:30m,5m:60m,15m:150m")
+	if err != nil {
+		return ts, err
+	}
+	wsp, err := whisper.Create(path, retentions, whisper.Sum, 0)
+	if err != nil {
+		return ts, err
+	}
+	defer wsp.Close()
+
+	rand.Seed(time.Now().Unix())
+	for i, _ := range ts {
+		dur := fmt.Sprintf("-%dm", 29-i)
+		tdur, _ := time.ParseDuration(dur)
+		point := new(whisper.TimeSeriesPoint)
+		j := rand.Intn(100)
+		if i == 4 {
+			point.Value = math.NaN()
+			point.Time = 0
+		} else {
+			point.Value = float64(j % 10)
+			point.Time = int(time.Now().Add(tdur).Unix())
+		}
+		ts[i] = point
+		//log.Printf("WhisperCreate(): point -%dm is %.2f\n", 29-i, point.Value)
+	}
+	wsp.UpdateMany(ts)
+
+	return ts, nil
+}
+
+func TestTwoArchives(t *testing.T) {
+	dataC, err := whisperCreateNullsManyArchives("c1.wsp")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Create an identical set of test data
+	err = whisperCreateDataMany("c2.wsp", dataC)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = whisperCreateDataMany("d1.wsp", dataC)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = whisperCreateDataMany("d2.wsp", dataC)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// whisper-fill.py needs to be in the PATH somewhere
+	log.Println("Running whisper-fill.py...")
+	c := exec.Command("whisper-fill.py", "c1.wsp", "d1.wsp")
+
+	reference_err := c.Run()
+	pythonFill, err := fetchFromFile("d1.wsp")
+
+	// Run my version
+	err = Files("c2.wsp", "d2.wsp", int(time.Now().Unix()))
+	if err != nil {
+		t.Error(err)
+	}
+	goFill, err := fetchFromFile("d2.wsp")
+	if err != nil {
+		t.Error(err)
+	}
+
+	// Compare to what we think our version should be
+	simuFill := simulateFill(dataC, dataC)
+	err = validateWhisper("d2.wsp", simuFill)
+	if err != nil {
+		t.Error(err)
+	}
+
+	// Validate the reference if whisper-fill.py was found
+	if reference_err == nil {
+		err = validateWhisper("d1.wsp", simuFill)
+		if err != nil {
+			t.Error(err)
+		}
+	}
+
+	if len(goFill) != len(pythonFill) {
+		t.Fatalf("length mismatch, python=%v, go=%v, expected=%v", len(goFill), len(pythonFill))
+	}
+
+	// Now try to print out a table of C, D, Python, Go, Simu
+	fmt.Printf("C     \tD     \tPython\tGo    \tSimu\n")
+	fmt.Printf("======\t======\t======\t======\t======\n")
+	for i := 0; i < len(goFill); i++ {
+		if reference_err != nil {
+			fmt.Printf("%6.1f\t%6.1f\t%6.1f\t%6.1f\t%6.1f\n", dataC[i].Value, dataC[i].Value, math.NaN(), goFill[i].Value, simuFill[i].Value)
+		} else {
+			fmt.Printf("%6.1f\t%6.1f\t%6.1f\t%6.1f\t%6.1f\n", dataC[i].Value, dataC[i].Value, pythonFill[i].Value, goFill[i].Value, simuFill[i].Value)
+		}
+	}
+	fmt.Println()
+}
+
 func TestReference(t *testing.T) {
 	// Create our random test data
 	dataA, err := whisperCreate("a1.wsp")