diff --git a/querier.go b/querier.go
index 0e0be2f6f..6d9f022a4 100644
--- a/querier.go
+++ b/querier.go
@@ -674,27 +674,25 @@ func (b *BufferedSeriesIterator) Seek(t int64) bool {
 
 	// If the delta would cause us to seek backwards, preserve the buffer
 	// and just continue regular advancment while filling the buffer on the way.
-	if t0 <= b.lastTime {
-		for b.Next() {
-			if tcur, _ := b.it.Values(); tcur >= t {
-				return true
-			}
+	if t0 > b.lastTime {
+		b.buf.reset()
+
+		ok := b.it.Seek(t0)
+		if !ok {
+			return false
 		}
-		return false
+		b.lastTime, _ = b.Values()
 	}
 
-	b.buf.reset()
-
-	ok := b.it.Seek(t0)
-	if !ok {
-		return false
+	if b.lastTime >= t {
+		return true
 	}
-
 	for b.Next() {
-		if ts, _ := b.Values(); ts >= t {
+		if b.lastTime >= t {
 			return true
 		}
 	}
+
 	return false
 }
 
@@ -704,7 +702,9 @@ func (b *BufferedSeriesIterator) Next() bool {
 	b.buf.add(b.it.Values())
 
 	ok := b.it.Next()
-	b.lastTime, _ = b.Values()
+	if ok {
+		b.lastTime, _ = b.Values()
+	}
 	return ok
 }
 
diff --git a/querier_test.go b/querier_test.go
index ed2dcbf23..86d3e310c 100644
--- a/querier_test.go
+++ b/querier_test.go
@@ -49,11 +49,15 @@ func (it *listSeriesIterator) Next() bool {
 }
 
 func (it *listSeriesIterator) Seek(t int64) bool {
+	if it.idx == -1 {
+		it.idx = 0
+	}
 	// Do binary search between current position and end.
 	it.idx = sort.Search(len(it.list)-it.idx, func(i int) bool {
 		s := it.list[i+it.idx]
 		return s.t >= t
 	})
+
 	return it.idx < len(it.list)
 }
 
@@ -283,3 +287,57 @@ func TestSampleRing(t *testing.T) {
 		}
 	}
 }
+
+func TestBufferedSeriesIterator(t *testing.T) {
+	var it *BufferedSeriesIterator
+
+	bufferEq := func(exp []sample) {
+		var b []sample
+		bit := it.Buffer()
+		for bit.Next() {
+			t, v := bit.Values()
+			b = append(b, sample{t: t, v: v})
+		}
+		require.Equal(t, exp, b, "buffer mismatch")
+	}
+	sampleEq := func(ets int64, ev float64) {
+		ts, v := it.Values()
+		require.Equal(t, ets, ts, "timestamp mismatch")
+		require.Equal(t, ev, v, "value mismatch")
+	}
+
+	it = NewBuffer(newListSeriesIterator([]sample{
+		{t: 1, v: 2},
+		{t: 2, v: 3},
+		{t: 3, v: 4},
+		{t: 4, v: 5},
+		{t: 5, v: 6},
+		{t: 99, v: 8},
+		{t: 100, v: 9},
+		{t: 101, v: 10},
+	}), 2)
+
+	require.True(t, it.Seek(-123), "seek failed")
+	sampleEq(1, 2)
+	bufferEq(nil)
+
+	require.True(t, it.Next(), "next failed")
+	sampleEq(2, 3)
+	bufferEq([]sample{{t: 1, v: 2}})
+
+	require.True(t, it.Next(), "next failed")
+	require.True(t, it.Next(), "next failed")
+	require.True(t, it.Next(), "next failed")
+	sampleEq(5, 6)
+	bufferEq([]sample{{t: 2, v: 3}, {t: 3, v: 4}, {t: 4, v: 5}})
+
+	require.True(t, it.Seek(5), "seek failed")
+	sampleEq(5, 6)
+	bufferEq([]sample{{t: 2, v: 3}, {t: 3, v: 4}, {t: 4, v: 5}})
+
+	require.True(t, it.Seek(101), "seek failed")
+	sampleEq(101, 10)
+	bufferEq([]sample{{t: 99, v: 8}, {t: 100, v: 9}})
+
+	require.False(t, it.Next(), "next succeeded unexpectedly")
+}