diff --git a/promql/lex.go b/promql/lex.go
index 41dee517c..eccd91bf4 100644
--- a/promql/lex.go
+++ b/promql/lex.go
@@ -465,7 +465,7 @@ func lexStatements(l *lexer) stateFn {
 			}
 		}
 		fallthrough
-	case isAlphaNumeric(r) || r == ':':
+	case isAlpha(r) || r == ':':
 		l.backup()
 		return lexKeywordOrIdentifier
 	case r == '(':
@@ -515,7 +515,7 @@ func lexInsideBraces(l *lexer) stateFn {
 		return l.errorf("unexpected end of input inside braces")
 	case isSpace(r):
 		return lexSpace
-	case unicode.IsLetter(r) || r == '_':
+	case isAlpha(r):
 		l.backup()
 		return lexIdentifier
 	case r == ',':
@@ -703,5 +703,10 @@ func isEndOfLine(r rune) bool {
 
 // isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
 func isAlphaNumeric(r rune) bool {
-	return r == '_' || ('a' <= r && r <= 'z') || ('A' <= r && r <= 'Z') || unicode.IsDigit(r)
+	return isAlpha(r) || unicode.IsDigit(r)
+}
+
+// isAlpha reports whether r is an alphabetic or underscore.
+func isAlpha(r rune) bool {
+	return r == '_' || ('a' <= r && r <= 'z') || ('A' <= r && r <= 'Z')
 }
diff --git a/promql/lex_test.go b/promql/lex_test.go
index 71dd9a988..ce56d83f6 100644
--- a/promql/lex_test.go
+++ b/promql/lex_test.go
@@ -121,6 +121,12 @@ var tests = []struct {
 	}, {
 		input:    "abc d",
 		expected: []item{{itemIdentifier, 0, "abc"}, {itemIdentifier, 4, "d"}},
+	}, {
+		input:    ":bc",
+		expected: []item{{itemMetricIdentifier, 0, ":bc"}},
+	}, {
+		input: "0a:bc",
+		fail:  true,
 	},
 	// Test comments.
 	{
@@ -247,6 +253,12 @@ var tests = []struct {
 	{
 		input: `台北`,
 		fail:  true,
+	}, {
+		input: `{台北='a'}`,
+		fail:  true,
+	}, {
+		input: `{0a='a'}`,
+		fail:  true,
 	}, {
 		input: `{foo='bar'}`,
 		expected: []item{
diff --git a/promql/parse.go b/promql/parse.go
index 58e5d8f3d..eeff1f7cc 100644
--- a/promql/parse.go
+++ b/promql/parse.go
@@ -453,6 +453,19 @@ func (p *parser) rangeSelector(vs *VectorSelector) *MatrixSelector {
 	return e
 }
 
+// parseNumber parses a number.
+func (p *parser) number(val string) float64 {
+	n, err := strconv.ParseInt(val, 0, 64)
+	f := float64(n)
+	if err != nil {
+		f, err = strconv.ParseFloat(val, 64)
+	}
+	if err != nil {
+		p.errorf("error parsing number: %s", err)
+	}
+	return f
+}
+
 // primaryExpr parses a primary expression.
 //
 //		<metric_name> | <function_call> | <vector_aggregation> | <literal>
@@ -460,14 +473,7 @@ func (p *parser) rangeSelector(vs *VectorSelector) *MatrixSelector {
 func (p *parser) primaryExpr() Expr {
 	switch t := p.next(); {
 	case t.typ == itemNumber:
-		n, err := strconv.ParseInt(t.val, 0, 64)
-		f := float64(n)
-		if err != nil {
-			f, err = strconv.ParseFloat(t.val, 64)
-		}
-		if err != nil {
-			p.errorf("error parsing number: %s", err)
-		}
+		f := p.number(t.val)
 		return &NumberLiteral{clientmodel.SampleValue(f)}
 
 	case t.typ == itemString: