diff --git a/promql/ast.go b/promql/ast.go
index fa9812fdd..3f929bbe2 100644
--- a/promql/ast.go
+++ b/promql/ast.go
@@ -231,9 +231,9 @@ type VectorMatching struct {
 	// MatchingLabels contains the labels which define equality of a pair of
 	// elements from the vectors.
 	MatchingLabels model.LabelNames
-	// Ignoring excludes the given label names from matching,
-	// rather than only using them.
-	Ignoring bool
+	// On includes the given label names from matching,
+	// rather than excluding them.
+	On bool
 	// Include contains additional labels that should be included in
 	// the result from the side with the lower cardinality.
 	Include model.LabelNames
diff --git a/promql/engine.go b/promql/engine.go
index 8a7ad6d66..92da4a41d 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -728,7 +728,7 @@ func (ev *evaluator) vectorAnd(lhs, rhs vector, matching *VectorMatching) vector
 	if matching.Card != CardManyToMany {
 		panic("set operations must only use many-to-many matching")
 	}
-	sigf := signatureFunc(matching.Ignoring, matching.MatchingLabels...)
+	sigf := signatureFunc(matching.On, matching.MatchingLabels...)
 
 	var result vector
 	// The set of signatures for the right-hand side vector.
@@ -751,7 +751,7 @@ func (ev *evaluator) vectorOr(lhs, rhs vector, matching *VectorMatching) vector
 	if matching.Card != CardManyToMany {
 		panic("set operations must only use many-to-many matching")
 	}
-	sigf := signatureFunc(matching.Ignoring, matching.MatchingLabels...)
+	sigf := signatureFunc(matching.On, matching.MatchingLabels...)
 
 	var result vector
 	leftSigs := map[uint64]struct{}{}
@@ -773,7 +773,7 @@ func (ev *evaluator) vectorUnless(lhs, rhs vector, matching *VectorMatching) vec
 	if matching.Card != CardManyToMany {
 		panic("set operations must only use many-to-many matching")
 	}
-	sigf := signatureFunc(matching.Ignoring, matching.MatchingLabels...)
+	sigf := signatureFunc(matching.On, matching.MatchingLabels...)
 
 	rightSigs := map[uint64]struct{}{}
 	for _, rs := range rhs {
@@ -796,7 +796,7 @@ func (ev *evaluator) vectorBinop(op itemType, lhs, rhs vector, matching *VectorM
 	}
 	var (
 		result = vector{}
-		sigf   = signatureFunc(matching.Ignoring, matching.MatchingLabels...)
+		sigf   = signatureFunc(matching.On, matching.MatchingLabels...)
 	)
 
 	// The control flow below handles one-to-one or many-to-one matching.
@@ -883,8 +883,8 @@ func (ev *evaluator) vectorBinop(op itemType, lhs, rhs vector, matching *VectorM
 
 // signatureFunc returns a function that calculates the signature for a metric
 // based on the provided labels. If ignoring, then the given labels are ignored instead.
-func signatureFunc(ignoring bool, labels ...model.LabelName) func(m metric.Metric) uint64 {
-	if len(labels) == 0 || ignoring {
+func signatureFunc(on bool, labels ...model.LabelName) func(m metric.Metric) uint64 {
+	if len(labels) == 0 || !on {
 		return func(m metric.Metric) uint64 {
 			tmp := m.Metric.Clone()
 			for _, l := range labels {
@@ -908,7 +908,7 @@ func resultMetric(lhs, rhs metric.Metric, op itemType, matching *VectorMatching)
 	if len(matching.MatchingLabels)+len(matching.Include) == 0 {
 		return lhs
 	}
-	if matching.Ignoring {
+	if !matching.On {
 		if matching.Card == CardOneToOne {
 			for _, l := range matching.MatchingLabels {
 				lhs.Del(l)
diff --git a/promql/parse.go b/promql/parse.go
index e2e03b18f..057237dae 100644
--- a/promql/parse.go
+++ b/promql/parse.go
@@ -463,8 +463,8 @@ func (p *parser) expr() Expr {
 
 		// Parse ON/IGNORING clause.
 		if p.peek().typ == itemOn || p.peek().typ == itemIgnoring {
-			if p.peek().typ == itemIgnoring {
-				vecMatching.Ignoring = true
+			if p.peek().typ == itemOn {
+				vecMatching.On = true
 			}
 			p.next()
 			vecMatching.MatchingLabels = p.labels()
@@ -485,7 +485,7 @@ func (p *parser) expr() Expr {
 
 		for _, ln := range vecMatching.MatchingLabels {
 			for _, ln2 := range vecMatching.Include {
-				if ln == ln2 && !vecMatching.Ignoring {
+				if ln == ln2 && vecMatching.On {
 					p.errorf("label %q must not occur in ON and GROUP clause at once", ln)
 				}
 			}
diff --git a/promql/parse_test.go b/promql/parse_test.go
index 4b9791fe2..16be4382c 100644
--- a/promql/parse_test.go
+++ b/promql/parse_test.go
@@ -471,12 +471,14 @@ var testExpr = []struct {
 				VectorMatching: &VectorMatching{
 					Card:           CardOneToMany,
 					MatchingLabels: model.LabelNames{"baz", "buz"},
+					On:             true,
 					Include:        model.LabelNames{"test"},
 				},
 			},
 			VectorMatching: &VectorMatching{
 				Card:           CardOneToOne,
 				MatchingLabels: model.LabelNames{"foo"},
+				On:             true,
 			},
 		},
 	}, {
@@ -498,6 +500,7 @@ var testExpr = []struct {
 			VectorMatching: &VectorMatching{
 				Card:           CardOneToOne,
 				MatchingLabels: model.LabelNames{"test", "blub"},
+				On:             true,
 			},
 		},
 	}, {
@@ -519,6 +522,7 @@ var testExpr = []struct {
 			VectorMatching: &VectorMatching{
 				Card:           CardManyToOne,
 				MatchingLabels: model.LabelNames{"test", "blub"},
+				On:             true,
 			},
 		},
 	}, {
@@ -540,6 +544,7 @@ var testExpr = []struct {
 			VectorMatching: &VectorMatching{
 				Card:           CardManyToMany,
 				MatchingLabels: model.LabelNames{"test", "blub"},
+				On:             true,
 			},
 		},
 	}, {
@@ -561,7 +566,6 @@ var testExpr = []struct {
 			VectorMatching: &VectorMatching{
 				Card:           CardManyToMany,
 				MatchingLabels: model.LabelNames{"test", "blub"},
-				Ignoring:       true,
 			},
 		},
 	}, {
@@ -583,6 +587,7 @@ var testExpr = []struct {
 			VectorMatching: &VectorMatching{
 				Card:           CardManyToMany,
 				MatchingLabels: model.LabelNames{"bar"},
+				On:             true,
 			},
 		},
 	}, {
@@ -604,6 +609,7 @@ var testExpr = []struct {
 			VectorMatching: &VectorMatching{
 				Card:           CardManyToOne,
 				MatchingLabels: model.LabelNames{"test", "blub"},
+				On:             true,
 				Include:        model.LabelNames{"bar"},
 			},
 		},
@@ -627,7 +633,6 @@ var testExpr = []struct {
 				Card:           CardManyToOne,
 				MatchingLabels: model.LabelNames{"test", "blub"},
 				Include:        model.LabelNames{"blub"},
-				Ignoring:       true,
 			},
 		},
 	}, {
@@ -650,7 +655,6 @@ var testExpr = []struct {
 				Card:           CardManyToOne,
 				MatchingLabels: model.LabelNames{"test", "blub"},
 				Include:        model.LabelNames{"bar"},
-				Ignoring:       true,
 			},
 		},
 	}, {
@@ -673,6 +677,7 @@ var testExpr = []struct {
 				Card:           CardOneToMany,
 				MatchingLabels: model.LabelNames{"test", "blub"},
 				Include:        model.LabelNames{"bar", "foo"},
+				On:             true,
 			},
 		},
 	}, {
@@ -695,7 +700,6 @@ var testExpr = []struct {
 				Card:           CardOneToMany,
 				MatchingLabels: model.LabelNames{"test", "blub"},
 				Include:        model.LabelNames{"bar", "foo"},
-				Ignoring:       true,
 			},
 		},
 	}, {
diff --git a/promql/printer.go b/promql/printer.go
index 5d395bf6b..8d93af29e 100644
--- a/promql/printer.go
+++ b/promql/printer.go
@@ -160,10 +160,10 @@ func (node *BinaryExpr) String() string {
 	matching := ""
 	vm := node.VectorMatching
 	if vm != nil && len(vm.MatchingLabels) > 0 {
-		if vm.Ignoring {
-			matching = fmt.Sprintf(" IGNORING(%s)", vm.MatchingLabels)
-		} else {
+		if vm.On {
 			matching = fmt.Sprintf(" ON(%s)", vm.MatchingLabels)
+		} else {
+			matching = fmt.Sprintf(" IGNORING(%s)", vm.MatchingLabels)
 		}
 		if vm.Card == CardManyToOne || vm.Card == CardOneToMany {
 			matching += " GROUP_"