diff --git a/src/generators/dom/Block.ts b/src/generators/dom/Block.ts
index d4ad5608f7..c23a80977c 100644
--- a/src/generators/dom/Block.ts
+++ b/src/generators/dom/Block.ts
@@ -1,5 +1,5 @@
 import CodeBuilder from '../../utils/CodeBuilder';
-import deindent from '../../utils/deindent.js';
+import deindent from '../../utils/deindent';
 import { DomGenerator } from './index';
 import { Node } from '../../interfaces';
 
diff --git a/src/generators/dom/index.ts b/src/generators/dom/index.ts
index 78258bac2b..096fe30307 100644
--- a/src/generators/dom/index.ts
+++ b/src/generators/dom/index.ts
@@ -3,7 +3,7 @@ import { parseExpressionAt } from 'acorn';
 import annotateWithScopes from '../../utils/annotateWithScopes';
 import isReference from '../../utils/isReference';
 import { walk } from 'estree-walker';
-import deindent from '../../utils/deindent.js';
+import deindent from '../../utils/deindent';
 import CodeBuilder from '../../utils/CodeBuilder';
 import visit from './visit';
 import shared from './shared';
diff --git a/src/generators/dom/visitors/Component/Binding.ts b/src/generators/dom/visitors/Component/Binding.ts
index 8de5379202..fa7d539a42 100644
--- a/src/generators/dom/visitors/Component/Binding.ts
+++ b/src/generators/dom/visitors/Component/Binding.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import flattenReference from '../../../../utils/flattenReference';
 import getSetter from '../shared/binding/getSetter';
 import { DomGenerator } from '../../index';
diff --git a/src/generators/dom/visitors/Component/Component.ts b/src/generators/dom/visitors/Component/Component.ts
index e107371a50..60c58602fe 100644
--- a/src/generators/dom/visitors/Component/Component.ts
+++ b/src/generators/dom/visitors/Component/Component.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import CodeBuilder from '../../../../utils/CodeBuilder';
 import visit from '../../visit';
 import visitAttribute from './Attribute';
diff --git a/src/generators/dom/visitors/Component/EventHandler.ts b/src/generators/dom/visitors/Component/EventHandler.ts
index ddc37da085..2db9549389 100644
--- a/src/generators/dom/visitors/Component/EventHandler.ts
+++ b/src/generators/dom/visitors/Component/EventHandler.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import { DomGenerator } from '../../index';
 import Block from '../../Block';
 import { Node } from '../../../../interfaces';
diff --git a/src/generators/dom/visitors/Component/Ref.ts b/src/generators/dom/visitors/Component/Ref.ts
index b966e81c71..3b9a929ed1 100644
--- a/src/generators/dom/visitors/Component/Ref.ts
+++ b/src/generators/dom/visitors/Component/Ref.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import { DomGenerator } from '../../index';
 import Block from '../../Block';
 import { Node } from '../../../../interfaces';
diff --git a/src/generators/dom/visitors/EachBlock.ts b/src/generators/dom/visitors/EachBlock.ts
index 27e639a0d1..25642b1865 100644
--- a/src/generators/dom/visitors/EachBlock.ts
+++ b/src/generators/dom/visitors/EachBlock.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../utils/deindent.js';
+import deindent from '../../../utils/deindent';
 import visit from '../visit';
 import { DomGenerator } from '../index';
 import Block from '../Block';
diff --git a/src/generators/dom/visitors/Element/Attribute.ts b/src/generators/dom/visitors/Element/Attribute.ts
index 8270852e11..7fbb73394b 100644
--- a/src/generators/dom/visitors/Element/Attribute.ts
+++ b/src/generators/dom/visitors/Element/Attribute.ts
@@ -1,5 +1,5 @@
 import attributeLookup from './lookup';
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import getStaticAttributeValue from './getStaticAttributeValue';
 import { DomGenerator } from '../../index';
 import Block from '../../Block';
diff --git a/src/generators/dom/visitors/Element/Binding.ts b/src/generators/dom/visitors/Element/Binding.ts
index a7c8d1aa1e..fdac104a87 100644
--- a/src/generators/dom/visitors/Element/Binding.ts
+++ b/src/generators/dom/visitors/Element/Binding.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import flattenReference from '../../../../utils/flattenReference';
 import getSetter from '../shared/binding/getSetter';
 import getStaticAttributeValue from './getStaticAttributeValue';
diff --git a/src/generators/dom/visitors/Element/Element.ts b/src/generators/dom/visitors/Element/Element.ts
index d5cb5c5bf1..a35177c073 100644
--- a/src/generators/dom/visitors/Element/Element.ts
+++ b/src/generators/dom/visitors/Element/Element.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import visit from '../../visit';
 import visitComponent from '../Component/Component';
 import visitWindow from './meta/Window';
diff --git a/src/generators/dom/visitors/Element/EventHandler.ts b/src/generators/dom/visitors/Element/EventHandler.ts
index aff7fb4ac0..660e64e395 100644
--- a/src/generators/dom/visitors/Element/EventHandler.ts
+++ b/src/generators/dom/visitors/Element/EventHandler.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import flattenReference from '../../../../utils/flattenReference';
 import { DomGenerator } from '../../index';
 import Block from '../../Block';
diff --git a/src/generators/dom/visitors/Element/Ref.ts b/src/generators/dom/visitors/Element/Ref.ts
index 6577114e6e..524c168e2b 100644
--- a/src/generators/dom/visitors/Element/Ref.ts
+++ b/src/generators/dom/visitors/Element/Ref.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import { DomGenerator } from '../../index';
 import Block from '../../Block';
 import { Node } from '../../../../interfaces';
diff --git a/src/generators/dom/visitors/Element/addTransitions.ts b/src/generators/dom/visitors/Element/addTransitions.ts
index 66d4a83cb9..358c6d7d6c 100644
--- a/src/generators/dom/visitors/Element/addTransitions.ts
+++ b/src/generators/dom/visitors/Element/addTransitions.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../utils/deindent.js';
+import deindent from '../../../../utils/deindent';
 import { DomGenerator } from '../../index';
 import Block from '../../Block';
 import { Node } from '../../../../interfaces';
diff --git a/src/generators/dom/visitors/Element/meta/Window.ts b/src/generators/dom/visitors/Element/meta/Window.ts
index 22127bd9f3..b1ddaa7709 100644
--- a/src/generators/dom/visitors/Element/meta/Window.ts
+++ b/src/generators/dom/visitors/Element/meta/Window.ts
@@ -1,5 +1,5 @@
 import flattenReference from '../../../../../utils/flattenReference';
-import deindent from '../../../../../utils/deindent.js';
+import deindent from '../../../../../utils/deindent';
 import { DomGenerator } from '../../../index';
 import Block from '../../../Block';
 import { Node } from '../../../../../interfaces';
diff --git a/src/generators/dom/visitors/IfBlock.ts b/src/generators/dom/visitors/IfBlock.ts
index 8f3700d4ef..7e294bc89f 100644
--- a/src/generators/dom/visitors/IfBlock.ts
+++ b/src/generators/dom/visitors/IfBlock.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../utils/deindent.js';
+import deindent from '../../../utils/deindent';
 import visit from '../visit';
 import { DomGenerator } from '../index';
 import Block from '../Block';
diff --git a/src/generators/dom/visitors/MustacheTag.ts b/src/generators/dom/visitors/MustacheTag.ts
index 21604778f5..febdb452e9 100644
--- a/src/generators/dom/visitors/MustacheTag.ts
+++ b/src/generators/dom/visitors/MustacheTag.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../utils/deindent.js';
+import deindent from '../../../utils/deindent';
 import { DomGenerator } from '../index';
 import Block from '../Block';
 import { Node } from '../../../interfaces';
diff --git a/src/generators/dom/visitors/RawMustacheTag.ts b/src/generators/dom/visitors/RawMustacheTag.ts
index 04c3c835d2..93c4aabace 100644
--- a/src/generators/dom/visitors/RawMustacheTag.ts
+++ b/src/generators/dom/visitors/RawMustacheTag.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../utils/deindent.js';
+import deindent from '../../../utils/deindent';
 import { DomGenerator } from '../index';
 import Block from '../Block';
 import { Node } from '../../../interfaces';
diff --git a/src/generators/dom/visitors/shared/binding/getSetter.ts b/src/generators/dom/visitors/shared/binding/getSetter.ts
index 6aa027e5f9..5cb4cc4c62 100644
--- a/src/generators/dom/visitors/shared/binding/getSetter.ts
+++ b/src/generators/dom/visitors/shared/binding/getSetter.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../../../utils/deindent.js';
+import deindent from '../../../../../utils/deindent';
 
 export default function getSetter({
 	block,
diff --git a/src/generators/server-side-rendering/Block.ts b/src/generators/server-side-rendering/Block.ts
index a8ebc029f5..1ad36fff5a 100644
--- a/src/generators/server-side-rendering/Block.ts
+++ b/src/generators/server-side-rendering/Block.ts
@@ -1,4 +1,4 @@
-import deindent from '../../utils/deindent.js';
+import deindent from '../../utils/deindent';
 import flattenReference from '../../utils/flattenReference';
 import { SsrGenerator } from './index';
 import { Node } from '../../interfaces';
diff --git a/src/generators/server-side-rendering/index.ts b/src/generators/server-side-rendering/index.ts
index d5b83f022b..32a4c6635e 100644
--- a/src/generators/server-side-rendering/index.ts
+++ b/src/generators/server-side-rendering/index.ts
@@ -1,4 +1,4 @@
-import deindent from '../../utils/deindent.js';
+import deindent from '../../utils/deindent';
 import Generator from '../Generator';
 import Block from './Block';
 import visit from './visit';
diff --git a/src/generators/shared/utils/getIntro.ts b/src/generators/shared/utils/getIntro.ts
index aea5f47062..7427f69a0b 100644
--- a/src/generators/shared/utils/getIntro.ts
+++ b/src/generators/shared/utils/getIntro.ts
@@ -1,4 +1,4 @@
-import deindent from '../../../utils/deindent.js';
+import deindent from '../../../utils/deindent';
 import getGlobals, { Globals } from './getGlobals';
 
 export type ModuleFormat = 'es' | 'amd' | 'cjs' | 'iife' | 'umd' | 'eval';
diff --git a/src/parse/read/directives.ts b/src/parse/read/directives.ts
index ad563df8c1..6064a61fcb 100644
--- a/src/parse/read/directives.ts
+++ b/src/parse/read/directives.ts
@@ -1,5 +1,5 @@
 import { parseExpressionAt } from 'acorn';
-import spaces from '../../utils/spaces.js';
+import spaces from '../../utils/spaces';
 import { Parser } from '../index';
 
 function readExpression(parser: Parser, start: number, quoteMark) {
diff --git a/src/parse/read/script.ts b/src/parse/read/script.ts
index c5a5f10b76..4d4a8559a1 100644
--- a/src/parse/read/script.ts
+++ b/src/parse/read/script.ts
@@ -1,5 +1,5 @@
 import { parse } from 'acorn';
-import spaces from '../../utils/spaces.js';
+import spaces from '../../utils/spaces';
 import { Parser } from '../index';
 
 const scriptClosingTag = '</script>';
diff --git a/src/utils/__test__.ts b/src/utils/__test__.ts
index 9f1cc87768..c1681dd8d6 100644
--- a/src/utils/__test__.ts
+++ b/src/utils/__test__.ts
@@ -1,5 +1,5 @@
 import * as assert from 'assert';
-import deindent from './deindent.js';
+import deindent from './deindent';
 import CodeBuilder from './CodeBuilder';
 
 describe('deindent', () => {
diff --git a/src/utils/deindent.js b/src/utils/deindent.ts
similarity index 89%
rename from src/utils/deindent.js
rename to src/utils/deindent.ts
index 6c335ca6f0..13278b26b1 100644
--- a/src/utils/deindent.js
+++ b/src/utils/deindent.ts
@@ -1,6 +1,6 @@
 const start = /\n(\t+)/;
 
-export default function deindent(strings, ...values) {
+export default function deindent(strings: string[], ...values: any[]) {
 	const indentation = start.exec(strings[0])[1];
 	const pattern = new RegExp(`^${indentation}`, 'gm');
 
@@ -34,7 +34,7 @@ export default function deindent(strings, ...values) {
 	return result.trim().replace(/\t+$/gm, '');
 }
 
-function getTrailingIndentation(str) {
+function getTrailingIndentation(str: string) {
 	let i = str.length;
 	while (str[i - 1] === ' ' || str[i - 1] === '\t') i -= 1;
 	return str.slice(i, str.length);
diff --git a/src/utils/getCodeFrame.ts b/src/utils/getCodeFrame.ts
index eb237841ae..39c54c7d60 100644
--- a/src/utils/getCodeFrame.ts
+++ b/src/utils/getCodeFrame.ts
@@ -1,4 +1,4 @@
-import spaces from './spaces.js';
+import spaces from './spaces';
 
 function tabsToSpaces(str: string) {
 	return str.replace(/^\t+/, match => match.split('\t').join('  '));
diff --git a/src/utils/spaces.js b/src/utils/spaces.ts
similarity index 59%
rename from src/utils/spaces.js
rename to src/utils/spaces.ts
index b1c7a47498..657c9c3884 100644
--- a/src/utils/spaces.js
+++ b/src/utils/spaces.ts
@@ -1,4 +1,4 @@
-export default function spaces(i) {
+export default function spaces(i: number) {
 	let result = '';
 	while (i--) result += ' ';
 	return result;
diff --git a/test/create/index.js b/test/create/index.js
index 9d5f5d1c02..3c2387d737 100644
--- a/test/create/index.js
+++ b/test/create/index.js
@@ -1,6 +1,5 @@
-import deindent from "../../src/utils/deindent.js";
 import assert from "assert";
-import { svelte } from "../helpers.js";
+import { svelte, deindent } from "../helpers.js";
 
 describe("create", () => {
 	it("should return a component constructor", () => {
diff --git a/test/formats/index.js b/test/formats/index.js
index cef98af74c..9d62bb712f 100644
--- a/test/formats/index.js
+++ b/test/formats/index.js
@@ -1,6 +1,5 @@
-import deindent from "../../src/utils/deindent.js";
 import assert from "assert";
-import { svelte, env, setupHtmlEqual } from "../helpers.js";
+import { svelte, deindent, env, setupHtmlEqual } from "../helpers.js";
 
 function testAmd(code, expectedId, dependencies, html) {
 	const fn = new Function("define", code);
diff --git a/test/helpers.js b/test/helpers.js
index 0ca921240e..d1601aa1e6 100644
--- a/test/helpers.js
+++ b/test/helpers.js
@@ -158,3 +158,50 @@ export function addLineNumbers(code) {
 		})
 		.join("\n");
 }
+
+const start = /\n(\t+)/;
+export function deindent(strings, ...values) {
+	const indentation = start.exec(strings[0])[1];
+	const pattern = new RegExp(`^${indentation}`, 'gm');
+
+	let result = strings[0].replace(start, '').replace(pattern, '');
+
+	let trailingIndentation = getTrailingIndentation(result);
+
+	for (let i = 1; i < strings.length; i += 1) {
+		let expression = values[i - 1];
+		const string = strings[i].replace(pattern, '');
+
+		if (Array.isArray(expression)) {
+			expression = expression.length ? expression.join('\n') : null;
+		}
+
+		if (expression || expression === '') {
+			const value = String(expression).replace(
+				/\n/g,
+				`\n${trailingIndentation}`
+			);
+			result += value + string;
+		} else {
+			let c = result.length;
+			while (/\s/.test(result[c - 1])) c -= 1;
+			result = result.slice(0, c) + string;
+		}
+
+		trailingIndentation = getTrailingIndentation(result);
+	}
+
+	return result.trim().replace(/\t+$/gm, '');
+}
+
+function getTrailingIndentation(str) {
+	let i = str.length;
+	while (str[i - 1] === ' ' || str[i - 1] === '\t') i -= 1;
+	return str.slice(i, str.length);
+}
+
+export function spaces(i) {
+	let result = '';
+	while (i--) result += ' ';
+	return result;
+}
diff --git a/test/runtime/index.js b/test/runtime/index.js
index 71588d6e71..eb33a506df 100644
--- a/test/runtime/index.js
+++ b/test/runtime/index.js
@@ -1,4 +1,3 @@
-import spaces from "../../src/utils/spaces.js";
 import assert from "assert";
 import * as path from "path";
 import * as fs from "fs";
@@ -11,7 +10,8 @@ import {
 	loadConfig,
 	loadSvelte,
 	env,
-	setupHtmlEqual
+	setupHtmlEqual,
+	spaces
 } from "../helpers.js";
 
 let svelte;