diff --git a/promql/lex.go b/promql/lex.go
index d3b611e90b..1c21d23fa6 100644
--- a/promql/lex.go
+++ b/promql/lex.go
@@ -550,6 +550,9 @@ func lexStatements(l *lexer) stateFn {
 		}
 		l.gotColon = false
 		l.emit(ItemLeftBracket)
+		if isSpace(l.peek()) {
+			skipSpaces(l)
+		}
 		l.bracketOpen = true
 		return lexDuration
 	case r == ']':
@@ -715,6 +718,14 @@ func digitVal(ch rune) int {
 	return 16 // Larger than any legal digit val.
 }
 
+// skipSpaces skips the spaces until a non-space is encountered.
+func skipSpaces(l *lexer) {
+	for isSpace(l.peek()) {
+		l.next()
+	}
+	l.ignore()
+}
+
 // lexString scans a quoted string. The initial quote has already been seen.
 func lexString(l *lexer) stateFn {
 Loop:
diff --git a/promql/lex_test.go b/promql/lex_test.go
index ef7231ad13..7b4b4a219e 100644
--- a/promql/lex_test.go
+++ b/promql/lex_test.go
@@ -49,6 +49,27 @@ var tests = []struct {
 					{ItemDuration, 1, `5m`},
 					{ItemRightBracket, 3, `]`},
 				},
+			}, {
+				input: "[ 5m]",
+				expected: []item{
+					{ItemLeftBracket, 0, `[`},
+					{ItemDuration, 2, `5m`},
+					{ItemRightBracket, 4, `]`},
+				},
+			}, {
+				input: "[  5m]",
+				expected: []item{
+					{ItemLeftBracket, 0, `[`},
+					{ItemDuration, 3, `5m`},
+					{ItemRightBracket, 5, `]`},
+				},
+			}, {
+				input: "[  5m ]",
+				expected: []item{
+					{ItemLeftBracket, 0, `[`},
+					{ItemDuration, 3, `5m`},
+					{ItemRightBracket, 6, `]`},
+				},
 			}, {
 				input:    "\r\n\r",
 				expected: []item{},
@@ -633,6 +654,15 @@ var tests = []struct {
 					{ItemRightBracket, 60, `]`},
 				},
 			},
+			{
+				input: `test:name[ 5m]`,
+				expected: []item{
+					{ItemMetricIdentifier, 0, `test:name`},
+					{ItemLeftBracket, 9, `[`},
+					{ItemDuration, 11, `5m`},
+					{ItemRightBracket, 13, `]`},
+				},
+			},
 			{
 				input: `test:name{o:n!~"bar"}[4m:4s]`,
 				fail:  true,