diff --git a/src/vs/base/common/strings.ts b/src/vs/base/common/strings.ts
index 1886577902bfe9fdfc9246e24601f96a7de9fb52..d79fcdfe5a18492874078f97b4457bd7fa6ff8dc 100644
--- a/src/vs/base/common/strings.ts
+++ b/src/vs/base/common/strings.ts
@@ -293,14 +293,14 @@ export function firstNonWhitespaceIndex(str: string): number {
  * Returns the leading whitespace of the string.
  * If the string contains only whitespaces, returns entire string
  */
-export function getLeadingWhitespace(str: string, from: number = 0): string {
-	for (let i = from, len = str.length; i < len; i++) {
+export function getLeadingWhitespace(str: string, start: number = 0, end: number = str.length): string {
+	for (let i = start; i < end; i++) {
 		let chCode = str.charCodeAt(i);
 		if (chCode !== CharCode.Space && chCode !== CharCode.Tab) {
-			return str.substring(from, i);
+			return str.substring(start, i);
 		}
 	}
-	return str.substr(from);
+	return str.substring(start, end);
 }
 
 /**
diff --git a/src/vs/base/test/common/strings.test.ts b/src/vs/base/test/common/strings.test.ts
index 7681a2e702c6e90bd3dbf645b36c836bdf1149fd..7b4efab9479d26a3eb548df782c3ffecbc61b775 100644
--- a/src/vs/base/test/common/strings.test.ts
+++ b/src/vs/base/test/common/strings.test.ts
@@ -310,7 +310,13 @@ suite('Strings', () => {
 	test('getLeadingWhitespace', () => {
 		assert.equal(strings.getLeadingWhitespace('  foo'), '  ');
 		assert.equal(strings.getLeadingWhitespace('  foo', 2), '');
+		assert.equal(strings.getLeadingWhitespace('  foo', 1, 1), '');
+		assert.equal(strings.getLeadingWhitespace('  foo', 0, 1), ' ');
 		assert.equal(strings.getLeadingWhitespace('  '), '  ');
 		assert.equal(strings.getLeadingWhitespace('  ', 1), ' ');
+		assert.equal(strings.getLeadingWhitespace('  ', 0, 1), ' ');
+		assert.equal(strings.getLeadingWhitespace('\t\tfunction foo(){', 0, 1), '\t');
+		assert.equal(strings.getLeadingWhitespace('\t\tfunction foo(){', 0, 2), '\t\t');
+
 	});
 });