diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a0dfba..f7ac67c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## 0.2.2 (2018-09-12)
+For hoast version 0.1.0.
+
+## Fixed
+- `engine` parameter had critical error in asynchronous operation.
+
 ## 0.2.1 (2018-09-12)
 For hoast version 0.1.0.
 
diff --git a/index.js b/index.js
index 4c05714..1aae556 100644
--- a/index.js
+++ b/index.js
@@ -39,18 +39,19 @@ module.exports = function(options) {
 	return async function(hoast, files) {
 		debug(`Running module.`);
 		
+		let filtered;
 		if (options.engine) {
 			debug(`Using engine filter method.`);
 			
-			Promise.all(files.map(function(file) {
+			await Promise.all(files.map(async function(file) {
 				// First check nanomatch filter whether it should be filtered.
 				if (options.patterns && nanomatch.any(file.path, options.patterns) === options.invert)  {
 					return true;
 				}
 				// Else use the specified engine function.
-				return options.engine(file);
+				return await options.engine(file);
 			})).then(function(result) {
-				files = files.filter(function(file, index) {
+				filtered = files.filter(function(file, index) {
 					return result[index];
 				});
 			});
@@ -58,13 +59,13 @@ module.exports = function(options) {
 			debug(`Using standard filter method.`);
 			
 			// Filter using nanomatch based of patterns.
-			files = files.filter(function(file) {
+			filtered = files.filter(function(file) {
 				debug(`Filtering file '${file.path}'.`);
 				return nanomatch.any(file.path, options.patterns) ? !options.invert : options.invert;
 			});
 		}
 		debug(`Finished filtering files.`);
 		
-		return files;
+		return filtered;
 	};
 };
\ No newline at end of file
diff --git a/package.json b/package.json
index f175863..aa5f282 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "author": "Ron Dekker",
   "name": "hoast-filter",
-  "version": "0.2.1",
+  "version": "0.2.2",
   "description": "Hoast module used to filter out files from further processing.",
   "license": "ISC",
   "keywords": [
diff --git a/test.js b/test.js
index 0172b89..a7df2b3 100644
--- a/test.js
+++ b/test.js
@@ -4,7 +4,7 @@ const test = require(`ava`);
 const Filter = require(`.`);
 
 // Test patterns option with a string.
-test(`pattern`, function(t) {
+test(`pattern`, async function(t) {
 	// Create dummy files.
 	let files = [{
 		path: `a.txt`
@@ -18,7 +18,7 @@ test(`pattern`, function(t) {
 	}];
 	
 	// Test module.
-	files = Filter({
+	files = await Filter({
 		patterns: `**/*.txt`
 	})({}, files);
 	
@@ -27,7 +27,7 @@ test(`pattern`, function(t) {
 });
 
 // Test patterns option with an array.
-test(`patterns`, function(t) {
+test(`patterns`, async function(t) {
 	// Create dummy files.
 	let files = [{
 		path: `a.txt`
@@ -45,7 +45,7 @@ test(`patterns`, function(t) {
 	}];
 	
 	// Test module.
-	files = Filter({
+	files = await Filter({
 		patterns: [
 			`**/*.txt`,
 			`**/*.md`
@@ -57,7 +57,7 @@ test(`patterns`, function(t) {
 });
 
 // Test invert option.
-test(`invert`, function(t) {
+test(`invert`, async function(t) {
 	// Create dummy files.
 	let files = [{
 		path: `a.txt`
@@ -73,7 +73,7 @@ test(`invert`, function(t) {
 	}];
 	
 	// Test module.
-	files = Filter({
+	files = await Filter({
 		invert: true,
 		patterns: [
 			`**/*.txt`,
@@ -86,7 +86,7 @@ test(`invert`, function(t) {
 });
 
 // Test engine option.
-test(`engine`, function(t) {
+test(`engine`, async function(t) {
 	// Create dummy files.
 	let files = [{
 		path: `a.txt`
@@ -102,7 +102,7 @@ test(`engine`, function(t) {
 	}];
 	
 	// Test module.
-	files = Filter({
+	files = await Filter({
 		engine: function(file) {
 			return file.path === `a.txt`;
 		}
@@ -113,7 +113,7 @@ test(`engine`, function(t) {
 });
 
 // Test engine option in combination with a pattern.
-test(`engine-pattern`, function(t) {
+test(`engine-pattern`, async function(t) {
 	// Create dummy files.
 	let files = [{
 		path: `a.txt`
@@ -131,7 +131,7 @@ test(`engine-pattern`, function(t) {
 	}];
 	
 	// Test module.
-	files = Filter({
+	files = await Filter({
 		engine: function(file) {
 			return file.path === `a.txt`;
 		},
@@ -143,7 +143,7 @@ test(`engine-pattern`, function(t) {
 });
 
 // Test engine option in combination with an inverted pattern.
-test(`engine-invert`, function(t) {
+test(`engine-invert`, async function(t) {
 	// Create dummy files.
 	let files = [{
 		path: `a.txt`
@@ -161,7 +161,7 @@ test(`engine-invert`, function(t) {
 	}];
 	
 	// Test module.
-	files = Filter({
+	files = await Filter({
 		engine: function(file) {
 			return file.path === `b.md`;
 		},