diff --git a/promql/lex.go b/promql/lex.go
index 5bbe843646..c3fd4e65e2 100644
--- a/promql/lex.go
+++ b/promql/lex.go
@@ -889,3 +889,16 @@ func isDigit(r rune) bool {
 func isAlpha(r rune) bool {
 	return r == '_' || ('a' <= r && r <= 'z') || ('A' <= r && r <= 'Z')
 }
+
+// isLabel reports whether the string can be used as label.
+func isLabel(s string) bool {
+	if len(s) == 0 || !isAlpha(rune(s[0])) {
+		return false
+	}
+	for _, c := range s[1:] {
+		if !isAlphaNumeric(c) {
+			return false
+		}
+	}
+	return true
+}
diff --git a/promql/parse.go b/promql/parse.go
index dbdc662ec5..6acaa11de3 100644
--- a/promql/parse.go
+++ b/promql/parse.go
@@ -673,7 +673,10 @@ func (p *parser) labels() model.LabelNames {
 	labels := model.LabelNames{}
 	if p.peek().typ != itemRightParen {
 		for {
-			id := p.expect(itemIdentifier, ctx)
+			id := p.next()
+			if !isLabel(id.val) {
+				p.errorf("unexpected %s in %s, expected label", id.desc(), ctx)
+			}
 			labels = append(labels, model.LabelName(id.val))
 
 			if p.peek().typ != itemComma {
diff --git a/promql/parse_test.go b/promql/parse_test.go
index 901c99ab3a..191cd39e17 100644
--- a/promql/parse_test.go
+++ b/promql/parse_test.go
@@ -1225,6 +1225,24 @@ var testExpr = []struct {
 			},
 			Param: &StringLiteral{"value"},
 		},
+	}, {
+		// Test usage of keywords as label names.
+		input: "sum without(and, by, avg, count, alert, annotations)(some_metric)",
+		expected: &AggregateExpr{
+			Op:      itemSum,
+			Without: true,
+			Expr: &VectorSelector{
+				Name: "some_metric",
+				LabelMatchers: metric.LabelMatchers{
+					mustLabelMatcher(metric.Equal, model.MetricNameLabel, "some_metric"),
+				},
+			},
+			Grouping: model.LabelNames{"and", "by", "avg", "count", "alert", "annotations"},
+		},
+	}, {
+		input:  "sum without(==)(some_metric)",
+		fail:   true,
+		errMsg: "unexpected <op:==> in grouping opts, expected label",
 	}, {
 		input:  `sum some_metric by (test)`,
 		fail:   true,