diff --git a/querier.go b/querier.go
index 26f839be1f..85bb7e75f3 100644
--- a/querier.go
+++ b/querier.go
@@ -370,6 +370,9 @@ func compareLabels(a, b Labels) int {
 		if d := strings.Compare(a[i].Name, b[i].Name); d != 0 {
 			return d
 		}
+		if d := strings.Compare(a[i].Value, b[i].Value); d != 0 {
+			return d
+		}
 	}
 	// If all labels so far were in common, the set with fewer labels comes first.
 	return len(a) - len(b)
diff --git a/querier_test.go b/querier_test.go
index 8e1a6f7364..19644257d0 100644
--- a/querier_test.go
+++ b/querier_test.go
@@ -211,6 +211,19 @@ func TestCompareLabels(t *testing.T) {
 			b:   []Label{{"aa", ""}, {"ab", ""}},
 			res: 1,
 		},
+		{
+			a: []Label{
+				{"__name__", "go_gc_duration_seconds"},
+				{"job", "prometheus"},
+				{"quantile", "0.75"},
+			},
+			b: []Label{
+				{"__name__", "go_gc_duration_seconds"},
+				{"job", "prometheus"},
+				{"quantile", "1"},
+			},
+			res: -1,
+		},
 	}
 	for _, c := range cases {
 		// Use constructor to ensure sortedness.
diff --git a/reader.go b/reader.go
index 4621e87d4b..b4faeb4c98 100644
--- a/reader.go
+++ b/reader.go
@@ -271,7 +271,7 @@ func (r *indexReader) Series(ref uint32, mint, maxt int64) (Series, error) {
 	// the underlying strings.
 	labels := make(Labels, 0, k)
 
-	for i := 0; i < int(k); i += 2 {
+	for i := 0; i < len(offsets); i += 2 {
 		n, err := r.lookupSymbol(offsets[i])
 		if err != nil {
 			return nil, errors.Wrap(err, "symbol lookup")