diff --git a/cmd/promtool/backfill.go b/cmd/promtool/backfill.go
index b3c33208d..6e7a98c55 100644
--- a/cmd/promtool/backfill.go
+++ b/cmd/promtool/backfill.go
@@ -77,9 +77,21 @@ func createBlocks(input []byte, mint, maxt int64, maxSamplesInAppender int, outp
 		returnErr = tsdb_errors.NewMulti(returnErr, db.Close()).Err()
 	}()
 
-	var wroteHeader bool
+	var (
+		wroteHeader  bool
+		nextSampleTs int64 = math.MaxInt64
+	)
 
 	for t := mint; t <= maxt; t = t + blockDuration {
+		tsUpper := t + blockDuration
+		if nextSampleTs != math.MaxInt64 && nextSampleTs >= tsUpper {
+			// The next sample is not in this timerange, we can avoid parsing
+			// the file for this timerange.
+			continue
+
+		}
+		nextSampleTs = math.MaxInt64
+
 		err := func() error {
 			w, err := tsdb.NewBlockWriter(log.NewNopLogger(), outputDir, blockDuration)
 			if err != nil {
@@ -92,7 +104,6 @@ func createBlocks(input []byte, mint, maxt int64, maxSamplesInAppender int, outp
 			ctx := context.Background()
 			app := w.Appender(ctx)
 			p := textparse.NewOpenMetricsParser(input)
-			tsUpper := t + blockDuration
 			samplesCount := 0
 			for {
 				e, err := p.Next()
@@ -106,15 +117,24 @@ func createBlocks(input []byte, mint, maxt int64, maxSamplesInAppender int, outp
 					continue
 				}
 
-				l := labels.Labels{}
-				p.Metric(&l)
 				_, ts, v := p.Series()
 				if ts == nil {
+					l := labels.Labels{}
+					p.Metric(&l)
 					return errors.Errorf("expected timestamp for series %v, got none", l)
 				}
-				if *ts < t || *ts >= tsUpper {
+				if *ts < t {
 					continue
 				}
+				if *ts >= tsUpper {
+					if *ts < nextSampleTs {
+						nextSampleTs = *ts
+					}
+					continue
+				}
+
+				l := labels.Labels{}
+				p.Metric(&l)
 
 				if _, err := app.Add(l, *ts, v); err != nil {
 					return errors.Wrap(err, "add sample")
diff --git a/cmd/promtool/backfill_test.go b/cmd/promtool/backfill_test.go
index 87f18d64b..56c3cf70c 100644
--- a/cmd/promtool/backfill_test.go
+++ b/cmd/promtool/backfill_test.go
@@ -150,6 +150,78 @@ http_requests_total{code="400"} 1 1565133713.990
 			ToParse: `# HELP http_requests_total The total number of HTTP requests.
 # TYPE http_requests_total counter
 http_requests_total{code="200"} 1021 1565133713.989
+http_requests_total{code="200"} 1022 1565392913.989
+http_requests_total{code="200"} 1023 1565652113.989
+# EOF
+`,
+			IsOk:                 true,
+			Description:          "Multiple samples separated by 3 days.",
+			MaxSamplesInAppender: 5000,
+			Expected: struct {
+				MinTime   int64
+				MaxTime   int64
+				NumBlocks int
+				Samples   []backfillSample
+			}{
+				MinTime:   1565133713989,
+				MaxTime:   1565652113989,
+				NumBlocks: 3,
+				Samples: []backfillSample{
+					{
+						Timestamp: 1565133713989,
+						Value:     1021,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "200"),
+					},
+					{
+						Timestamp: 1565392913989,
+						Value:     1022,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "200"),
+					},
+					{
+						Timestamp: 1565652113989,
+						Value:     1023,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "200"),
+					},
+				},
+			},
+		},
+		{
+			ToParse: `# TYPE go info
+go_info{version="go1.15.3"} 1 1565392913.989
+# TYPE http_requests_total counter
+http_requests_total{code="200"} 1021 1565133713.989
+# EOF
+`,
+			IsOk:                 true,
+			Description:          "Unordered samples from multiple series, which end in different blocks.",
+			MaxSamplesInAppender: 5000,
+			Expected: struct {
+				MinTime   int64
+				MaxTime   int64
+				NumBlocks int
+				Samples   []backfillSample
+			}{
+				MinTime:   1565133713989,
+				MaxTime:   1565392913989,
+				NumBlocks: 2,
+				Samples: []backfillSample{
+					{
+						Timestamp: 1565133713989,
+						Value:     1021,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "200"),
+					},
+					{
+						Timestamp: 1565392913989,
+						Value:     1,
+						Labels:    labels.FromStrings("__name__", "go_info", "version", "go1.15.3"),
+					},
+				},
+			},
+		},
+		{
+			ToParse: `# HELP http_requests_total The total number of HTTP requests.
+# TYPE http_requests_total counter
+http_requests_total{code="200"} 1021 1565133713.989
 http_requests_total{code="200"} 1 1565133714.989
 http_requests_total{code="400"} 2 1565133715.989
 # EOF