diff --git a/block.go b/block.go
index 1d5ebfb1..664ead49 100644
--- a/block.go
+++ b/block.go
@@ -447,7 +447,7 @@ Outer:
 		}
 
 		for _, chk := range chks {
-			if intervalOverlap(mint, maxt, chk.MinTime, chk.MaxTime) {
+			if chk.OverlapsClosedInterval(mint, maxt) {
 				// Delete only until the current values and not beyond.
 				tmin, tmax := clampInterval(mint, maxt, chks[0].MinTime, chks[len(chks)-1].MaxTime)
 				stones[p.At()] = Intervals{{tmin, tmax}}
@@ -539,6 +539,13 @@ func (pb *Block) Snapshot(dir string) error {
 	return nil
 }
 
+// Returns true if the block overlaps [mint, maxt].
+func (pb *Block) OverlapsClosedInterval(mint, maxt int64) bool {
+	// The block itself is a half-open interval
+	// [pb.meta.MinTime, pb.meta.MaxTime).
+	return pb.meta.MinTime <= maxt && mint < pb.meta.MaxTime
+}
+
 func clampInterval(a, b, mint, maxt int64) (int64, int64) {
 	if a < mint {
 		a = mint
diff --git a/chunks/chunks.go b/chunks/chunks.go
index 795740ff..5eab2398 100644
--- a/chunks/chunks.go
+++ b/chunks/chunks.go
@@ -57,6 +57,12 @@ func (cm *Meta) writeHash(h hash.Hash) error {
 	return nil
 }
 
+// Returns true if the chunk overlaps [mint, maxt].
+func (cm *Meta) OverlapsClosedInterval(mint, maxt int64) bool {
+	// The chunk itself is a closed interval [cm.MinTime, cm.MaxTime].
+	return cm.MinTime <= maxt && mint <= cm.MaxTime
+}
+
 var (
 	errInvalidSize     = fmt.Errorf("invalid size")
 	errInvalidFlag     = fmt.Errorf("invalid flag")
diff --git a/compact.go b/compact.go
index 8743c8ba..aae8cc1c 100644
--- a/compact.go
+++ b/compact.go
@@ -592,7 +592,7 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 		if len(dranges) > 0 {
 			// Re-encode the chunk to not have deleted values.
 			for i, chk := range chks {
-				if !intervalOverlap(dranges[0].Mint, dranges[len(dranges)-1].Maxt, chk.MinTime, chk.MaxTime) {
+				if !chk.OverlapsClosedInterval(dranges[0].Mint, dranges[len(dranges)-1].Maxt) {
 					continue
 				}
 
diff --git a/db.go b/db.go
index 28fafc09..fcfbeeeb 100644
--- a/db.go
+++ b/db.go
@@ -360,7 +360,13 @@ func (db *DB) compact() (changes bool, err error) {
 		head := &rangeHead{
 			head: db.head,
 			mint: mint,
-			maxt: maxt,
+			// We remove 1 millisecond from maxt because block
+			// intervals are half-open: [b.MinTime, b.MaxTime). But
+			// chunk intervals are closed: [c.MinTime, c.MaxTime];
+			// so in order to make sure that overlaps are evaluated
+			// consistently, we explicitly remove the last value
+			// from the block interval here.
+			maxt: maxt - 1,
 		}
 		if _, err = db.compactor.Write(db.dir, head, mint, maxt, nil); err != nil {
 			return changes, errors.Wrap(err, "persist head block")
@@ -756,8 +762,7 @@ func (db *DB) Querier(mint, maxt int64) (Querier, error) {
 	defer db.mtx.RUnlock()
 
 	for _, b := range db.blocks {
-		m := b.Meta()
-		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
+		if b.OverlapsClosedInterval(mint, maxt) {
 			blocks = append(blocks, b)
 		}
 	}
@@ -799,8 +804,7 @@ func (db *DB) Delete(mint, maxt int64, ms ...labels.Matcher) error {
 	defer db.mtx.RUnlock()
 
 	for _, b := range db.blocks {
-		m := b.Meta()
-		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
+		if b.OverlapsClosedInterval(mint, maxt) {
 			g.Go(func(b *Block) func() error {
 				return func() error { return b.Delete(mint, maxt, ms...) }
 			}(b))
@@ -848,11 +852,6 @@ func (db *DB) CleanTombstones() (err error) {
 	return errors.Wrap(db.reload(), "reload blocks")
 }
 
-func intervalOverlap(amin, amax, bmin, bmax int64) bool {
-	// Checks Overlap: http://stackoverflow.com/questions/3269434/
-	return amin <= bmax && bmin <= amax
-}
-
 func isBlockDir(fi os.FileInfo) bool {
 	if !fi.IsDir() {
 		return false
diff --git a/db_test.go b/db_test.go
index 72817a10..7ed21aac 100644
--- a/db_test.go
+++ b/db_test.go
@@ -26,6 +26,8 @@ import (
 
 	"github.com/oklog/ulid"
 	"github.com/pkg/errors"
+	"github.com/prometheus/tsdb/chunks"
+	"github.com/prometheus/tsdb/index"
 	"github.com/prometheus/tsdb/labels"
 	"github.com/prometheus/tsdb/testutil"
 )
@@ -1096,3 +1098,90 @@ func TestOverlappingBlocksDetectsAllOverlaps(t *testing.T) {
 		{Min: 8, Max: 9}: {nc1[8], nc1[9]},                                 // 7-10, 8-9
 	}, OverlappingBlocks(nc1))
 }
+
+// Regression test for https://github.com/prometheus/tsdb/issues/347
+func TestChunkAtBlockBoundary(t *testing.T) {
+	db, close := openTestDB(t, nil)
+	defer close()
+	defer db.Close()
+
+	app := db.Appender()
+
+	blockRange := DefaultOptions.BlockRanges[0]
+	label := labels.FromStrings("foo", "bar")
+
+	for i := int64(0); i < 3; i++ {
+		_, err := app.Add(label, i*blockRange, 0)
+		testutil.Ok(t, err)
+		_, err = app.Add(label, i*blockRange+1000, 0)
+		testutil.Ok(t, err)
+	}
+
+	err := app.Commit()
+	testutil.Ok(t, err)
+
+	_, err = db.compact()
+	testutil.Ok(t, err)
+
+	for _, block := range db.blocks {
+		r, err := block.Index()
+		testutil.Ok(t, err)
+		defer r.Close()
+
+		meta := block.Meta()
+
+		p, err := r.Postings(index.AllPostingsKey())
+		testutil.Ok(t, err)
+
+		var (
+			lset labels.Labels
+			chks []chunks.Meta
+		)
+
+		chunkCount := 0
+
+		for p.Next() {
+			err = r.Series(p.At(), &lset, &chks)
+			testutil.Ok(t, err)
+			for _, c := range chks {
+				testutil.Assert(t, meta.MinTime <= c.MinTime && c.MaxTime <= meta.MaxTime,
+					"chunk spans beyond block boundaries: [block.MinTime=%d, block.MaxTime=%d]; [chunk.MinTime=%d, chunk.MaxTime=%d]",
+					meta.MinTime, meta.MaxTime, c.MinTime, c.MaxTime)
+				chunkCount++
+			}
+		}
+		testutil.Assert(t, chunkCount == 1, "expected 1 chunk in block %s, got %d", meta.ULID, chunkCount)
+	}
+}
+
+func TestQuerierWithBoundaryChunks(t *testing.T) {
+	db, close := openTestDB(t, nil)
+	defer close()
+	defer db.Close()
+
+	app := db.Appender()
+
+	blockRange := DefaultOptions.BlockRanges[0]
+	label := labels.FromStrings("foo", "bar")
+
+	for i := int64(0); i < 5; i++ {
+		_, err := app.Add(label, i*blockRange, 0)
+		testutil.Ok(t, err)
+	}
+
+	err := app.Commit()
+	testutil.Ok(t, err)
+
+	_, err = db.compact()
+	testutil.Ok(t, err)
+
+	testutil.Assert(t, len(db.blocks) >= 3, "invalid test, less than three blocks in DB")
+
+	q, err := db.Querier(blockRange, 2*blockRange)
+	testutil.Ok(t, err)
+	defer q.Close()
+
+	// The requested interval covers 2 blocks, so the querier should contain 2 blocks.
+	count := len(q.(*querier).blocks)
+	testutil.Assert(t, count == 2, "expected 2 blocks in querier, got %d", count)
+}
diff --git a/head.go b/head.go
index e8a4582f..c694d20c 100644
--- a/head.go
+++ b/head.go
@@ -735,19 +735,14 @@ func (h *headChunkReader) Chunk(ref uint64) (chunkenc.Chunk, error) {
 	s.Lock()
 	c := s.chunk(int(cid))
 
-	// This means that the chunk has been garbage collected.
-	if c == nil {
+	// This means that the chunk has been garbage collected or is outside
+	// the specified range.
+	if c == nil || !c.OverlapsClosedInterval(h.mint, h.maxt) {
 		s.Unlock()
 		return nil, ErrNotFound
 	}
-
-	mint, maxt := c.minTime, c.maxTime
 	s.Unlock()
 
-	// Do not expose chunks that are outside of the specified range.
-	if c == nil || !intervalOverlap(mint, maxt, h.mint, h.maxt) {
-		return nil, ErrNotFound
-	}
 	return &safeChunk{
 		Chunk: c.chunk,
 		s:     s,
@@ -852,7 +847,7 @@ func (h *headIndexReader) Series(ref uint64, lbls *labels.Labels, chks *[]chunks
 
 	for i, c := range s.chunks {
 		// Do not expose chunks that are outside of the specified range.
-		if !intervalOverlap(c.minTime, c.maxTime, h.mint, h.maxt) {
+		if !c.OverlapsClosedInterval(h.mint, h.maxt) {
 			continue
 		}
 		*chks = append(*chks, chunks.Meta{
@@ -1291,6 +1286,11 @@ type memChunk struct {
 	minTime, maxTime int64
 }
 
+// Returns true if the chunk overlaps [mint, maxt].
+func (mc *memChunk) OverlapsClosedInterval(mint, maxt int64) bool {
+	return mc.minTime <= maxt && mint <= mc.maxTime
+}
+
 type memSafeIterator struct {
 	chunkenc.Iterator