diff --git a/Gruntfile.js b/Gruntfile.js
index 4efcd11..febecc5 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -348,6 +348,16 @@ module.exports = function(grunt) {
 					stylesheets: ['css', 'scss', 'less']
 				}
 			},
+			filename_length: {
+				src: 'test/src_filename_length/*.svg',
+				dest: 'test/tmp/filename_length',
+				options: {
+					autoHint: false,
+					engine: 'node',
+					hashes: false,
+					types: 'woff'
+				}
+			},
 		},
 		nodeunit: {
 			all: ['test/webfont_test.js']
diff --git a/tasks/webfont.js b/tasks/webfont.js
index 742c458..e793f21 100755
--- a/tasks/webfont.js
+++ b/tasks/webfont.js
@@ -622,7 +622,7 @@ module.exports = function(grunt) {
 		 * @return {Integer}
 		 */
 		function getNextCodepoint() {
-			while (_.includes(o.codepoints, currentCodepoint)) {
+			while (_.invert(o.codepoints).hasOwnProperty(currentCodepoint)) {
 				currentCodepoint++;
 			}
 			return currentCodepoint;
diff --git a/test/src_filename_length/length.svg b/test/src_filename_length/length.svg
new file mode 100644
index 0000000..b87aebe
--- /dev/null
+++ b/test/src_filename_length/length.svg
@@ -0,0 +1,2 @@
+<!-- Generated by IcoMoon.io -->
+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 512 512"><title>length</title><path d="M460.704 263.248l-76.56-77.472v54.336h-111.648v-176.112h-48v176.112h-111.648v-54.336l-77.552 77.472 77.168 77.808 0.384-53.632h111.648v176.576h48v-176.576h111.648l-0.624 53.632z"></path></svg>
diff --git a/test/webfont_test.js b/test/webfont_test.js
index f8bde54..550c79c 100644
--- a/test/webfont_test.js
+++ b/test/webfont_test.js
@@ -915,6 +915,20 @@ exports.webfont = {
 		// Files should render with custom context variables
 		test.ok(fs.existsSync('test/tmp/custom_output/context-test.html'));
 
+		test.done();
+	},
+
+	filename_length: function(test) {
+
+		// File should have been created.
+		test.ok(fs.existsSync('test/tmp/filename_length/icons.css'));
+
+		// File should have been created.
+		test.ok(fs.existsSync('test/tmp/filename_length/icons.woff'));
+
+		// File should have been created.
+		test.ok(fs.existsSync('test/tmp/filename_length/icons.html'));
+
 		test.done();
 	}