diff --git a/promql/engine.go b/promql/engine.go
index 0225f78d2..0455779a4 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -1567,7 +1567,7 @@ func (ev *evaluator) eval(expr parser.Expr) (parser.Value, storage.Warnings) {
 
 	case *parser.NumberLiteral:
 		return ev.rangeEval(nil, func(v []parser.Value, _ [][]EvalSeriesHelper, enh *EvalNodeHelper) (Vector, storage.Warnings) {
-			return append(enh.Out, Sample{Point: Point{V: e.Val}}), nil
+			return append(enh.Out, Sample{Point: Point{V: e.Val}, Metric: labels.EmptyLabels()}), nil
 		})
 
 	case *parser.StringLiteral:
@@ -2190,7 +2190,7 @@ func resultMetric(lhs, rhs labels.Labels, op parser.ItemType, matching *parser.V
 		}
 	}
 
-	ret := enh.lb.Labels(nil)
+	ret := enh.lb.Labels(labels.EmptyLabels())
 	enh.resultMetric[str] = ret
 	return ret
 }
@@ -2230,7 +2230,7 @@ func (ev *evaluator) VectorscalarBinop(op parser.ItemType, lhs Vector, rhs Scala
 }
 
 func dropMetricName(l labels.Labels) labels.Labels {
-	return labels.NewBuilder(l).Del(labels.MetricName).Labels(nil)
+	return labels.NewBuilder(l).Del(labels.MetricName).Labels(labels.EmptyLabels())
 }
 
 // scalarBinop evaluates a binary operation between two Scalars.
@@ -2357,7 +2357,7 @@ func (ev *evaluator) aggregation(op parser.ItemType, grouping []string, without
 		}
 	}
 
-	lb := labels.NewBuilder(nil)
+	lb := labels.NewBuilder(labels.EmptyLabels())
 	var buf []byte
 	for si, s := range vec {
 		metric := s.Metric
@@ -2365,7 +2365,7 @@ func (ev *evaluator) aggregation(op parser.ItemType, grouping []string, without
 		if op == parser.COUNT_VALUES {
 			lb.Reset(metric)
 			lb.Set(valueLabel, strconv.FormatFloat(s.V, 'f', -1, 64))
-			metric = lb.Labels(nil)
+			metric = lb.Labels(labels.EmptyLabels())
 
 			// We've changed the metric so we have to recompute the grouping key.
 			recomputeGroupingKey = true
@@ -2389,7 +2389,7 @@ func (ev *evaluator) aggregation(op parser.ItemType, grouping []string, without
 			} else {
 				lb.Keep(grouping...)
 			}
-			m := lb.Labels(nil)
+			m := lb.Labels(labels.EmptyLabels())
 			newAgg := &groupedAggregation{
 				labels:     m,
 				value:      s.V,
diff --git a/promql/functions.go b/promql/functions.go
index d481cb735..c5922002b 100644
--- a/promql/functions.go
+++ b/promql/functions.go
@@ -957,7 +957,7 @@ func funcHistogramQuantile(vals []parser.Value, args parser.Expressions, enh *Ev
 		if !ok {
 			sample.Metric = labels.NewBuilder(sample.Metric).
 				Del(excludedLabels...).
-				Labels(nil)
+				Labels(labels.EmptyLabels())
 
 			mb = &metricWithBuckets{sample.Metric, nil}
 			enh.signatureToMetricWithBuckets[string(enh.lblBuf)] = mb
@@ -1077,7 +1077,7 @@ func funcLabelReplace(vals []parser.Value, args parser.Expressions, enh *EvalNod
 				if len(res) > 0 {
 					lb.Set(dst, string(res))
 				}
-				outMetric = lb.Labels(nil)
+				outMetric = lb.Labels(labels.EmptyLabels())
 				enh.Dmn[h] = outMetric
 			}
 		}
@@ -1145,7 +1145,7 @@ func funcLabelJoin(vals []parser.Value, args parser.Expressions, enh *EvalNodeHe
 				lb.Set(dst, strval)
 			}
 
-			outMetric = lb.Labels(nil)
+			outMetric = lb.Labels(labels.EmptyLabels())
 			enh.Dmn[h] = outMetric
 		}
 
@@ -1383,7 +1383,7 @@ func (s *vectorByReverseValueHeap) Pop() interface{} {
 // createLabelsForAbsentFunction returns the labels that are uniquely and exactly matched
 // in a given expression. It is used in the absent functions.
 func createLabelsForAbsentFunction(expr parser.Expr) labels.Labels {
-	m := labels.Labels{}
+	b := labels.NewBuilder(labels.EmptyLabels())
 
 	var lm []*labels.Matcher
 	switch n := expr.(type) {
@@ -1392,25 +1392,26 @@ func createLabelsForAbsentFunction(expr parser.Expr) labels.Labels {
 	case *parser.MatrixSelector:
 		lm = n.VectorSelector.(*parser.VectorSelector).LabelMatchers
 	default:
-		return m
+		return labels.EmptyLabels()
 	}
 
-	empty := []string{}
+	// The 'has' map implements backwards-compatibility for historic behaviour:
+	// e.g. in `absent(x{job="a",job="b",foo="bar"})` then `job` is removed from the output.
+	// Note this gives arguably wrong behaviour for `absent(x{job="a",job="a",foo="bar"})`.
+	has := make(map[string]bool, len(lm))
 	for _, ma := range lm {
 		if ma.Name == labels.MetricName {
 			continue
 		}
-		if ma.Type == labels.MatchEqual && !m.Has(ma.Name) {
-			m = labels.NewBuilder(m).Set(ma.Name, ma.Value).Labels(nil)
+		if ma.Type == labels.MatchEqual && !has[ma.Name] {
+			b.Set(ma.Name, ma.Value)
+			has[ma.Name] = true
 		} else {
-			empty = append(empty, ma.Name)
+			b.Del(ma.Name)
 		}
 	}
 
-	for _, v := range empty {
-		m = labels.NewBuilder(m).Del(v).Labels(nil)
-	}
-	return m
+	return b.Labels(labels.EmptyLabels())
 }
 
 func stringFromArg(e parser.Expr) string {
diff --git a/promql/parser/generated_parser.y b/promql/parser/generated_parser.y
index 433f45259..461e854ac 100644
--- a/promql/parser/generated_parser.y
+++ b/promql/parser/generated_parser.y
@@ -16,13 +16,13 @@ package parser
 
 import (
         "math"
-        "sort"
         "strconv"
         "time"
 
         "github.com/prometheus/prometheus/model/labels"
         "github.com/prometheus/prometheus/model/value"
 )
+
 %}
 
 %union {
@@ -32,6 +32,7 @@ import (
     matcher   *labels.Matcher
     label     labels.Label
     labels    labels.Labels
+    lblList   []labels.Label
     strings   []string
     series    []SequenceValue
     uint      uint64
@@ -138,10 +139,9 @@ START_METRIC_SELECTOR
 // Type definitions for grammar rules.
 %type <matchers> label_match_list
 %type <matcher> label_matcher
-
 %type <item> aggregate_op grouping_label match_op maybe_label metric_identifier unary_op at_modifier_preprocessors
-
-%type <labels> label_set label_set_list metric
+%type <labels> label_set metric
+%type <lblList> label_set_list
 %type <label> label_set_item
 %type <strings> grouping_label_list grouping_labels maybe_grouping_labels
 %type <series> series_item series_values
@@ -567,7 +567,7 @@ label_matcher   : IDENTIFIER match_op STRING
  */
 
 metric          : metric_identifier label_set
-                        { $$ = append($2, labels.Label{Name: labels.MetricName, Value: $1.Val}); sort.Sort($$) }
+                        { b := labels.NewBuilder($2); b.Set(labels.MetricName, $1.Val); $$ = b.Labels(labels.EmptyLabels()) }
                 | label_set
                         {$$ = $1}
                 ;
diff --git a/promql/parser/generated_parser.y.go b/promql/parser/generated_parser.y.go
index 87f25f024..3a0e8bf69 100644
--- a/promql/parser/generated_parser.y.go
+++ b/promql/parser/generated_parser.y.go
@@ -9,7 +9,6 @@ import __yyfmt__ "fmt"
 
 import (
 	"math"
-	"sort"
 	"strconv"
 	"time"
 
@@ -26,6 +25,7 @@ type yySymType struct {
 	matcher  *labels.Matcher
 	label    labels.Label
 	labels   labels.Labels
+	lblList  []labels.Label
 	strings  []string
 	series   []SequenceValue
 	uint     uint64
@@ -458,7 +458,7 @@ var yyPact = [...]int{
 
 var yyPgo = [...]int{
 	0, 267, 7, 265, 2, 264, 262, 164, 261, 257,
-	115, 253, 181, 8, 252, 4, 5, 251, 250, 0,
+	115, 181, 253, 8, 252, 4, 5, 251, 250, 0,
 	23, 248, 6, 247, 246, 245, 10, 64, 244, 239,
 	1, 231, 230, 9, 217, 21, 214, 213, 205, 201,
 	198, 196, 189, 188, 206, 3, 180, 165, 127,
@@ -474,10 +474,10 @@ var yyR1 = [...]int{
 	31, 33, 33, 32, 32, 32, 40, 38, 38, 38,
 	24, 24, 24, 9, 9, 36, 42, 42, 42, 42,
 	42, 43, 44, 44, 44, 35, 35, 35, 1, 1,
-	1, 2, 2, 2, 2, 12, 12, 7, 7, 7,
+	1, 2, 2, 2, 2, 11, 11, 7, 7, 7,
 	7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
 	7, 7, 7, 7, 7, 7, 7, 7, 7, 10,
-	10, 10, 10, 11, 11, 11, 13, 13, 13, 13,
+	10, 10, 10, 12, 12, 12, 13, 13, 13, 13,
 	48, 18, 18, 18, 18, 17, 17, 17, 17, 17,
 	21, 21, 21, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 6, 6, 6, 6, 6,
@@ -513,14 +513,14 @@ var yyR2 = [...]int{
 }
 
 var yyChk = [...]int{
-	-1000, -47, 75, 76, 77, 78, 2, 10, -12, -7,
+	-1000, -47, 75, 76, 77, 78, 2, 10, -11, -7,
 	-10, 47, 48, 62, 49, 50, 51, 12, 32, 33,
 	36, 52, 16, 53, 66, 54, 55, 56, 57, 58,
-	68, 71, 72, 13, -48, -12, 10, -30, -25, -28,
+	68, 71, 72, 13, -48, -11, 10, -30, -25, -28,
 	-31, -36, -37, -38, -40, -41, -42, -43, -44, -24,
 	-3, 12, 17, 15, 23, -8, -7, -35, 47, 48,
 	49, 50, 51, 52, 53, 54, 55, 56, 57, 58,
-	26, 42, 13, -44, -10, -11, 18, -13, 12, 2,
+	26, 42, 13, -44, -10, -12, 18, -13, 12, 2,
 	-18, 2, 26, 44, 27, 28, 30, 31, 32, 33,
 	34, 35, 36, 37, 38, 39, 41, 42, 66, 43,
 	14, -26, -33, 2, 62, 68, 15, -33, -30, -30,
@@ -1492,8 +1492,9 @@ yydefault:
 		yyDollar = yyS[yypt-2 : yypt+1]
 //line promql/parser/generated_parser.y:570
 		{
-			yyVAL.labels = append(yyDollar[2].labels, labels.Label{Name: labels.MetricName, Value: yyDollar[1].item.Val})
-			sort.Sort(yyVAL.labels)
+			b := labels.NewBuilder(yyDollar[2].labels)
+			b.Set(labels.MetricName, yyDollar[1].item.Val)
+			yyVAL.labels = b.Labels(labels.EmptyLabels())
 		}
 	case 96:
 		yyDollar = yyS[yypt-1 : yypt+1]
@@ -1505,13 +1506,13 @@ yydefault:
 		yyDollar = yyS[yypt-3 : yypt+1]
 //line promql/parser/generated_parser.y:579
 		{
-			yyVAL.labels = labels.New(yyDollar[2].labels...)
+			yyVAL.labels = labels.New(yyDollar[2].lblList...)
 		}
 	case 120:
 		yyDollar = yyS[yypt-4 : yypt+1]
 //line promql/parser/generated_parser.y:581
 		{
-			yyVAL.labels = labels.New(yyDollar[2].labels...)
+			yyVAL.labels = labels.New(yyDollar[2].lblList...)
 		}
 	case 121:
 		yyDollar = yyS[yypt-2 : yypt+1]
@@ -1529,20 +1530,20 @@ yydefault:
 		yyDollar = yyS[yypt-3 : yypt+1]
 //line promql/parser/generated_parser.y:589
 		{
-			yyVAL.labels = append(yyDollar[1].labels, yyDollar[3].label)
+			yyVAL.lblList = append(yyDollar[1].lblList, yyDollar[3].label)
 		}
 	case 124:
 		yyDollar = yyS[yypt-1 : yypt+1]
 //line promql/parser/generated_parser.y:591
 		{
-			yyVAL.labels = []labels.Label{yyDollar[1].label}
+			yyVAL.lblList = []labels.Label{yyDollar[1].label}
 		}
 	case 125:
 		yyDollar = yyS[yypt-2 : yypt+1]
 //line promql/parser/generated_parser.y:593
 		{
 			yylex.(*parser).unexpected("label set", "\",\" or \"}\"")
-			yyVAL.labels = yyDollar[1].labels
+			yyVAL.lblList = yyDollar[1].lblList
 		}
 	case 126:
 		yyDollar = yyS[yypt-3 : yypt+1]
diff --git a/promql/test.go b/promql/test.go
index ab2a159c4..344c59c07 100644
--- a/promql/test.go
+++ b/promql/test.go
@@ -202,7 +202,7 @@ func (t *Test) parseEval(lines []string, i int) (int, *evalCmd, error) {
 			break
 		}
 		if f, err := parseNumber(defLine); err == nil {
-			cmd.expect(0, nil, parser.SequenceValue{Value: f})
+			cmd.expect(0, labels.EmptyLabels(), parser.SequenceValue{Value: f})
 			break
 		}
 		metric, vals, err := parser.ParseSeriesDesc(defLine)
@@ -371,7 +371,7 @@ func (ev *evalCmd) String() string {
 // expect adds a new metric with a sequence of values to the set of expected
 // results for the query.
 func (ev *evalCmd) expect(pos int, m labels.Labels, vals ...parser.SequenceValue) {
-	if m == nil {
+	if m.IsEmpty() {
 		ev.expected[0] = entry{pos: pos, vals: vals}
 		return
 	}