diff --git a/compact.go b/compact.go
index 1036cf403..751edf4f1 100644
--- a/compact.go
+++ b/compact.go
@@ -229,11 +229,24 @@ func splitByRange(ds []dirMeta, tr int64) [][]dirMeta {
 
 	for i := 0; i < len(ds); {
 		var group []dirMeta
+		var t0 int64
+		m := ds[i].meta
 		// Compute start of aligned time range of size tr closest to the current block's start.
-		t0 := ds[i].meta.MinTime - (ds[i].meta.MinTime % tr)
+		if m.MinTime >= 0 {
+			t0 = tr * (m.MinTime / tr)
+		} else {
+			t0 = tr * ((m.MinTime - tr + 1) / tr)
+		}
+		// Skip blocks that don't fall into the range. This can happen via mis-alignment or
+		// by being the multiple of the intended range.
+		if ds[i].meta.MinTime < t0 || ds[i].meta.MaxTime > t0+tr {
+			i++
+			continue
+		}
 
 		// Add all dirs to the current group that are within [t0, t0+tr].
 		for ; i < len(ds); i++ {
+			// Either the block falls into the next range or doesn't fit at all (checked above).
 			if ds[i].meta.MinTime < t0 || ds[i].meta.MaxTime > t0+tr {
 				break
 			}
diff --git a/compact_test.go b/compact_test.go
index 07d3f6d63..25b931a1e 100644
--- a/compact_test.go
+++ b/compact_test.go
@@ -14,7 +14,6 @@
 package tsdb
 
 import (
-	"sort"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -178,58 +177,84 @@ func TestCompactionSelect(t *testing.T) {
 }
 
 func TestSplitByRange(t *testing.T) {
-	splitterFunc := func(ds []dirMeta, tr int64) [][]dirMeta {
-		rMap := make(map[int64][]dirMeta)
-		for _, dir := range ds {
-			t0 := dir.meta.MinTime - dir.meta.MinTime%tr
-			if intervalContains(t0, t0+tr, dir.meta.MinTime) && intervalContains(t0, t0+tr, dir.meta.MaxTime) {
-				rMap[t0] = append(rMap[t0], dir)
-			}
-		}
-		res := make([][]dirMeta, 0, len(rMap))
-		for _, v := range rMap {
-			res = append(res, v)
-		}
-
-		sort.Slice(res, func(i, j int) bool {
-			return res[i][0].meta.MinTime < res[j][0].meta.MinTime
-		})
-
-		return res
-	}
-
 	cases := []struct {
 		trange int64
-		ranges [][]int64
-		output [][][]int64
+		ranges [][2]int64
+		output [][][2]int64
 	}{
 		{
 			trange: 60,
-			ranges: [][]int64{{0, 10}},
+			ranges: [][2]int64{{0, 10}},
+			output: [][][2]int64{
+				{{0, 10}},
+			},
 		},
 		{
 			trange: 60,
-			ranges: [][]int64{{0, 60}},
+			ranges: [][2]int64{{0, 60}},
+			output: [][][2]int64{
+				{{0, 60}},
+			},
 		},
 		{
 			trange: 60,
-			ranges: [][]int64{{0, 10}, {30, 60}},
+			ranges: [][2]int64{{0, 10}, {9, 15}, {30, 60}},
+			output: [][][2]int64{
+				{{0, 10}, {9, 15}, {30, 60}},
+			},
 		},
 		{
 			trange: 60,
-			ranges: [][]int64{{0, 10}, {60, 90}},
+			ranges: [][2]int64{{70, 90}, {125, 130}, {130, 180}, {1000, 1001}},
+			output: [][][2]int64{
+				{{70, 90}},
+				{{125, 130}, {130, 180}},
+				{{1000, 1001}},
+			},
+		},
+		// Mis-aligned or too-large blocks are ignored.
+		{
+			trange: 60,
+			ranges: [][2]int64{{50, 70}, {70, 80}},
+			output: [][][2]int64{
+				{{70, 80}},
+			},
+		},
+		{
+			trange: 72,
+			ranges: [][2]int64{{0, 144}, {144, 216}, {216, 288}},
+			output: [][][2]int64{
+				{{144, 216}},
+				{{216, 288}},
+			},
+		},
+		// Various awkward edge cases easy to hit with negative numbers.
+		{
+			trange: 60,
+			ranges: [][2]int64{{-10, -5}},
+			output: [][][2]int64{
+				{{-10, -5}},
+			},
 		},
 		{
 			trange: 60,
-			ranges: [][]int64{{0, 10}, {20, 30}, {90, 120}},
+			ranges: [][2]int64{{-60, -50}, {-10, -5}},
+			output: [][][2]int64{
+				{{-60, -50}, {-10, -5}},
+			},
 		},
 		{
 			trange: 60,
-			ranges: [][]int64{{0, 10}, {59, 60}, {60, 120}, {120, 180}, {190, 200}, {200, 210}, {220, 239}},
+			ranges: [][2]int64{{-60, -50}, {-10, -5}, {0, 15}},
+			output: [][][2]int64{
+				{{-60, -50}, {-10, -5}},
+				{{0, 15}},
+			},
 		},
 	}
 
 	for _, c := range cases {
+		// Transform input range tuples into dirMetas.
 		blocks := make([]dirMeta, 0, len(c.ranges))
 		for _, r := range c.ranges {
 			blocks = append(blocks, dirMeta{
@@ -240,6 +265,16 @@ func TestSplitByRange(t *testing.T) {
 			})
 		}
 
-		require.Equal(t, splitterFunc(blocks, c.trange), splitByRange(blocks, c.trange))
+		// Transform output range tuples into dirMetas.
+		exp := make([][]dirMeta, len(c.output))
+		for i, group := range c.output {
+			for _, r := range group {
+				exp[i] = append(exp[i], dirMeta{
+					meta: &BlockMeta{MinTime: r[0], MaxTime: r[1]},
+				})
+			}
+		}
+
+		require.Equal(t, exp, splitByRange(blocks, c.trange))
 	}
 }