diff --git a/promql/lex.go b/promql/lex.go
index 935c2d8a2..189d58ac2 100644
--- a/promql/lex.go
+++ b/promql/lex.go
@@ -724,7 +724,7 @@ Loop:
 }
 
 func isSpace(r rune) bool {
-	return r == ' ' || r == '\t' || r == '\n'
+	return r == ' ' || r == '\t' || r == '\n' || r == '\r'
 }
 
 // isEndOfLine reports whether r is an end-of-line character.
diff --git a/promql/lex_test.go b/promql/lex_test.go
index c12f75327..7ef474033 100644
--- a/promql/lex_test.go
+++ b/promql/lex_test.go
@@ -42,6 +42,9 @@ var tests = []struct {
 			{itemDuration, 1, `5m`},
 			{itemRightBracket, 3, `]`},
 		},
+	}, {
+		input:    "\r\n\r",
+		expected: []item{},
 	},
 	// Test numbers.
 	{