diff --git a/CHANGELOG.md b/CHANGELOG.md
index 88870e9fb03..1778deeacab 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@
 ### Jsonnet
 
 ### Mimirtool
+* [BUGFIX] Fix out of bounds error on export with large timespans and/or series count. #5700
 
 ### Mimir Continuous Test
 
diff --git a/pkg/mimirtool/backfill/backfill.go b/pkg/mimirtool/backfill/backfill.go
index c3320c9b319..fe20400bd24 100644
--- a/pkg/mimirtool/backfill/backfill.go
+++ b/pkg/mimirtool/backfill/backfill.go
@@ -90,7 +90,7 @@ func CreateBlocks(input IteratorCreator, mint, maxt int64, maxSamplesInAppender
 
 	var wroteHeader bool
 
-	for t := mint; t <= maxt; t = t + blockDuration {
+	for t := mint; t <= maxt; t = t + blockDuration/2 {
 		err := func() error {
 			w, err := tsdb.NewBlockWriter(log.NewNopLogger(), outputDir, blockDuration)
 			if err != nil {
@@ -106,7 +106,7 @@ func CreateBlocks(input IteratorCreator, mint, maxt int64, maxSamplesInAppender
 			ctx := context.Background()
 			app := w.Appender(ctx)
 			i := input()
-			tsUpper := t + blockDuration
+			tsUpper := t + blockDuration/2
 			samplesCount := 0
 			for {
 				err := i.Next()
diff --git a/pkg/mimirtool/commands/remote_read.go b/pkg/mimirtool/commands/remote_read.go
index ec6d6d8f862..4bfb8bd117b 100644
--- a/pkg/mimirtool/commands/remote_read.go
+++ b/pkg/mimirtool/commands/remote_read.go
@@ -416,8 +416,7 @@ func (c *RemoteReadCommand) export(_ *kingpin.ParseContext) error {
 	if err != nil {
 		return err
 	}
-
-	iterator := func() backfill.Iterator {
+	iteratorCreator := func() backfill.Iterator {
 		return newTimeSeriesIterator(timeseries)
 	}
 
@@ -434,7 +433,7 @@ func (c *RemoteReadCommand) export(_ *kingpin.ParseContext) error {
 	defer pipeR.Close()
 
 	log.Infof("Store TSDB blocks in '%s'", c.tsdbPath)
-	if err := backfill.CreateBlocks(iterator, int64(mint), int64(maxt), 1000, c.tsdbPath, true, pipeW); err != nil {
+	if err := backfill.CreateBlocks(iteratorCreator, int64(mint), int64(maxt), 1000, c.tsdbPath, true, pipeW); err != nil {
 		return err
 	}
 
diff --git a/pkg/mimirtool/commands/remote_read_test.go b/pkg/mimirtool/commands/remote_read_test.go
index 45ae17b943a..8c589fa7782 100644
--- a/pkg/mimirtool/commands/remote_read_test.go
+++ b/pkg/mimirtool/commands/remote_read_test.go
@@ -6,12 +6,16 @@
 package commands
 
 import (
+	"fmt"
 	"io"
 	"testing"
+	"time"
 
 	"github.com/pkg/errors"
 	"github.com/prometheus/prometheus/prompb"
 	"github.com/stretchr/testify/assert"
+
+	"github.com/grafana/mimir/pkg/mimirtool/backfill"
 )
 
 func TestTimeSeriesIterator(t *testing.T) {
@@ -150,3 +154,41 @@ func TestTimeSeriesIterator(t *testing.T) {
 	}
 
 }
+
+// TestEarlyCommit writes samples of many series that don't fit into the same
+// append commit. It makes sure that batching the samples into many commits
+// doesn't cause the appends to advance the head block too far and make future
+// appends invalid.
+func TestEarlyCommit(t *testing.T) {
+	maxSamplesPerBlock := 1000
+	series := 100
+	samples := 140
+
+	start := int64(time.Date(2023, 8, 30, 11, 42, 17, 0, time.UTC).UnixNano())
+	inc := int64(time.Minute / time.Millisecond)
+	end := start + (inc * int64(samples))
+	ts := make([]*prompb.TimeSeries, series)
+	for i := 0; i < series; i++ {
+		s := &prompb.TimeSeries{
+			Labels: []prompb.Label{
+				{
+					Name:  "__name__",
+					Value: fmt.Sprintf("metric_%d", i),
+				},
+			},
+			Samples: make([]prompb.Sample, samples),
+		}
+		for j := 0; j < samples; j++ {
+			s.Samples[j] = prompb.Sample{
+				Value:     float64(j),
+				Timestamp: start + (inc * int64(j)),
+			}
+		}
+		ts[i] = s
+	}
+	iterator := func() backfill.Iterator {
+		return newTimeSeriesIterator(ts)
+	}
+	err := backfill.CreateBlocks(iterator, start, end, maxSamplesPerBlock, t.TempDir(), true, io.Discard)
+	assert.NoError(t, err)
+}