diff --git a/CHANGELOG.md b/CHANGELOG.md
index c8dfefc1a9..4423537567 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6098](https://github.com/thanos-io/thanos/pull/6098) Cache/Redis: upgrade `rueidis` to v0.0.93 to fix potential panic when the client-side caching is disabled.
 - [#6103](https://github.com/thanos-io/thanos/pull/6103) Mixins(Rule): Fix query for long rule evaluations.
 - [#6121](https://github.com/thanos-io/thanos/pull/6121) Receive: Deduplicate metamonitoring queries.
+- [#6137](https://github.com/thanos-io/thanos/pull/6137) Downsample: Repair of non-empty XOR chunks during 1h downsampling.
 
 ### Changed
 
diff --git a/pkg/compact/downsample/downsample.go b/pkg/compact/downsample/downsample.go
index 07cf294f06..d55c95f449 100644
--- a/pkg/compact/downsample/downsample.go
+++ b/pkg/compact/downsample/downsample.go
@@ -167,10 +167,22 @@ func Downsample(
 						// https://github.com/thanos-io/thanos/issues/5272
 						level.Warn(logger).Log("msg", fmt.Sprintf("expected downsampled chunk (*downsample.AggrChunk) got an empty %T instead for series: %d", c.Chunk, postings.At()))
 						continue
+					} else {
+						if err := expandChunkIterator(c.Chunk.Iterator(reuseIt), &all); err != nil {
+							return id, errors.Wrapf(err, "expand chunk %d, series %d", c.Ref, postings.At())
+						}
+						aggrDataChunks := DownsampleRaw(all, ResLevel1)
+						for _, cn := range aggrDataChunks {
+							ac, ok = cn.Chunk.(*AggrChunk)
+							if !ok {
+								return id, errors.New("Not able to convert non-empty XOR chunks to 5m downsampled aggregated chunks.")
+							}
+						}
 					}
-					return id, errors.Errorf("expected downsampled chunk (*downsample.AggrChunk) got a non-empty %T instead for series: %d", c.Chunk, postings.At())
+
 				}
 				aggrChunks = append(aggrChunks, ac)
+
 			}
 			downsampledChunks, err := downsampleAggr(
 				aggrChunks,
diff --git a/pkg/compact/downsample/downsample_test.go b/pkg/compact/downsample/downsample_test.go
index d86f610007..14c4d4dea8 100644
--- a/pkg/compact/downsample/downsample_test.go
+++ b/pkg/compact/downsample/downsample_test.go
@@ -538,21 +538,23 @@ func TestDownsampleAggrAndEmptyXORChunks(t *testing.T) {
 }
 
 func TestDownsampleAggrAndNonEmptyXORChunks(t *testing.T) {
+
 	logger := log.NewLogfmtLogger(os.Stderr)
 	dir := t.TempDir()
-
 	ser := &series{lset: labels.FromStrings("__name__", "a")}
 	aggr := map[AggrType][]sample{
-		AggrCount:   {{t: 1587690299999, v: 20}, {t: 1587690599999, v: 20}, {t: 1587690899999, v: 20}, {t: 1587691199999, v: 20}, {t: 1587691499999, v: 20}, {t: 1587691799999, v: 20}, {t: 1587692099999, v: 20}, {t: 1587692399999, v: 20}, {t: 1587692699999, v: 16}, {t: 1587692999999, v: 20}, {t: 1587693299999, v: 20}, {t: 1587693590791, v: 20}},
-		AggrSum:     {{t: 1587690299999, v: 9.276972e+06}, {t: 1587690599999, v: 9.359861e+06}, {t: 1587690899999, v: 9.447457e+06}, {t: 1587691199999, v: 9.542732e+06}, {t: 1587691499999, v: 9.630379e+06}, {t: 1587691799999, v: 9.715631e+06}, {t: 1587692099999, v: 9.799808e+06}, {t: 1587692399999, v: 9.888117e+06}, {t: 1587692699999, v: 2.98928e+06}, {t: 1587692999999, v: 81592}, {t: 1587693299999, v: 163711}, {t: 1587693590791, v: 255746}},
-		AggrMin:     {{t: 1587690299999, v: 461968}, {t: 1587690599999, v: 466070}, {t: 1587690899999, v: 470131}, {t: 1587691199999, v: 474913}, {t: 1587691499999, v: 479625}, {t: 1587691799999, v: 483709}, {t: 1587692099999, v: 488036}, {t: 1587692399999, v: 492223}, {t: 1587692699999, v: 75}, {t: 1587692999999, v: 2261}, {t: 1587693299999, v: 6210}, {t: 1587693590791, v: 10464}},
-		AggrMax:     {{t: 1587690299999, v: 465870}, {t: 1587690599999, v: 469951}, {t: 1587690899999, v: 474726}, {t: 1587691199999, v: 479368}, {t: 1587691499999, v: 483566}, {t: 1587691799999, v: 487787}, {t: 1587692099999, v: 492065}, {t: 1587692399999, v: 496245}, {t: 1587692699999, v: 496544}, {t: 1587692999999, v: 6010}, {t: 1587693299999, v: 10242}, {t: 1587693590791, v: 14956}},
-		AggrCounter: {{t: 1587690005791, v: 461968}, {t: 1587690299999, v: 465870}, {t: 1587690599999, v: 469951}, {t: 1587690899999, v: 474726}, {t: 1587691199999, v: 479368}, {t: 1587691499999, v: 483566}, {t: 1587691799999, v: 487787}, {t: 1587692099999, v: 492065}, {t: 1587692399999, v: 496245}, {t: 1587692699999, v: 498647}, {t: 1587692999999, v: 502554}, {t: 1587693299999, v: 506786}, {t: 1587693590791, v: 511500}, {t: 1587693590791, v: 14956}},
+		AggrCount:   {{t: 1587690299999, v: 20}, {t: 1587690599999, v: 20}, {t: 1587690899999, v: 20}},
+		AggrSum:     {{t: 1587690299999, v: 9.276972e+06}, {t: 1587690599999, v: 9.359861e+06}, {t: 1587693590791, v: 255746}},
+		AggrMin:     {{t: 1587690299999, v: 461968}, {t: 1587690599999, v: 466070}, {t: 1587690899999, v: 470131}, {t: 1587691199999, v: 474913}},
+		AggrMax:     {{t: 1587690299999, v: 465870}, {t: 1587690599999, v: 469951}, {t: 1587690899999, v: 474726}},
+		AggrCounter: {{t: 1587690005791, v: 461968}, {t: 1587690299999, v: 465870}, {t: 1587690599999, v: 469951}},
 	}
 	raw := chunkenc.NewXORChunk()
 	app, err := raw.Appender()
 	testutil.Ok(t, err)
+
 	app.Append(1587690005794, 42.5)
+
 	ser.chunks = append(ser.chunks, encodeTestAggrSeries(aggr), chunks.Meta{
 		MinTime: math.MaxInt64,
 		MaxTime: math.MinInt64,
@@ -566,7 +568,64 @@ func TestDownsampleAggrAndNonEmptyXORChunks(t *testing.T) {
 	fakeMeta.Thanos.Downsample.Resolution = 300_000
 	id, err := Downsample(logger, fakeMeta, mb, dir, 3_600_000)
 	_ = id
-	testutil.NotOk(t, err)
+	testutil.Ok(t, err)
+
+	expected := []map[AggrType][]sample{
+		{
+			AggrCount:   {{1587690005794, 20}, {1587690005794, 20}, {1587690005794, 21}},
+			AggrSum:     {{1587690005794, 9.276972e+06}, {1587690005794, 9.359861e+06}, {1587690005794, 255788.5}},
+			AggrMin:     {{1587690005794, 461968}, {1587690005794, 466070}, {1587690005794, 470131}, {1587690005794, 42.5}},
+			AggrMax:     {{1587690005794, 465870}, {1587690005794, 469951}, {1587690005794, 474726}},
+			AggrCounter: {{1587690005791, 461968}, {1587690599999, 469951}, {1587690599999, 469951}},
+		},
+	}
+
+	_, err = metadata.ReadFromDir(filepath.Join(dir, id.String()))
+	testutil.Ok(t, err)
+
+	indexr, err := index.NewFileReader(filepath.Join(dir, id.String(), block.IndexFilename))
+	testutil.Ok(t, err)
+	defer func() { testutil.Ok(t, indexr.Close()) }()
+
+	chunkr, err := chunks.NewDirReader(filepath.Join(dir, id.String(), block.ChunksDirname), NewPool())
+	testutil.Ok(t, err)
+	defer func() { testutil.Ok(t, chunkr.Close()) }()
+
+	pall, err := indexr.Postings(index.AllPostingsKey())
+	testutil.Ok(t, err)
+
+	var series []storage.SeriesRef
+	for pall.Next() {
+		series = append(series, pall.At())
+	}
+	testutil.Ok(t, pall.Err())
+	testutil.Equals(t, 1, len(series))
+
+	var builder labels.ScratchBuilder
+	var chks []chunks.Meta
+	testutil.Ok(t, indexr.Series(series[0], &builder, &chks))
+
+	var got []map[AggrType][]sample
+	for _, c := range chks {
+		chk, err := chunkr.Chunk(c)
+		testutil.Ok(t, err)
+
+		m := map[AggrType][]sample{}
+		for _, at := range []AggrType{AggrCount, AggrSum, AggrMin, AggrMax, AggrCounter} {
+			c, err := chk.(*AggrChunk).Get(at)
+			if err == ErrAggrNotExist {
+				continue
+			}
+			testutil.Ok(t, err)
+
+			buf := m[at]
+			testutil.Ok(t, expandChunkIterator(c.Iterator(nil), &buf))
+			m[at] = buf
+		}
+		got = append(got, m)
+	}
+	testutil.Equals(t, expected, got)
+
 }
 
 func chunksToSeriesIteratable(t *testing.T, inRaw [][]sample, inAggr []map[AggrType][]sample) *series {