diff --git a/.travis.yml b/.travis.yml
index fbaf2e8..f2ead47 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,6 @@ language: php
 
 php:
   - 5.6
-  - 7.1
   - 7.2
   - 7.3
   - 7.4
diff --git a/composer.json b/composer.json
index d32a5d4..f96d98d 100644
--- a/composer.json
+++ b/composer.json
@@ -30,7 +30,7 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.3"
+        "phpunit/phpunit": ">=4.8.35 <8"
     },
     "scripts": {
         "test": "phpunit"
diff --git a/lessc.inc.php b/lessc.inc.php
index 4764b28..14299d1 100644
--- a/lessc.inc.php
+++ b/lessc.inc.php
@@ -1,7 +1,7 @@
 <?php
 
 /**
- * lessphp v0.5.2
+ * lessphp v0.5.4
  * http://leafo.net/lessphp
  *
  * LESS CSS compiler, adapted from http://lesscss.org
@@ -39,7 +39,7 @@
  * handling things like indentation.
  */
 class lessc {
-	static public $VERSION = "v0.5.2";
+	static public $VERSION = "v0.5.4";
 
 	static public $TRUE = array("keyword", "true");
 	static public $FALSE = array("keyword", "false");
@@ -758,7 +758,7 @@ protected function compileProp($prop, $block, $out) {
 					if ($suffix !== null &&
 						$subProp[0] == "assign" &&
 						is_string($subProp[1]) &&
-						$subProp[1]{0} != $this->vPrefix)
+						$subProp[1][0] != $this->vPrefix)
 					{
 						$subProp[2] = array(
 							'list', ' ',
@@ -2759,7 +2759,7 @@ protected function parseChunk() {
 				$hidden = true;
 				if (!isset($block->args)) {
 					foreach ($block->tags as $tag) {
-						if (!is_string($tag) || $tag{0} != $this->lessc->mPrefix) {
+						if (!is_string($tag) || $tag[0] != $this->lessc->mPrefix) {
 							$hidden = false;
 							break;
 						}
@@ -2813,7 +2813,7 @@ protected function isDirective($dirname, $directives) {
 	protected function fixTags($tags) {
 		// move @ tags out of variable namespace
 		foreach ($tags as &$tag) {
-			if ($tag{0} == $this->lessc->vPrefix)
+			if ($tag[0] == $this->lessc->vPrefix)
 				$tag[0] = $this->lessc->mPrefix;
 		}
 		return $tags;
diff --git a/tests/ApiTest.php b/tests/ApiTest.php
index fe1bbff..8e0a6f4 100644
--- a/tests/ApiTest.php
+++ b/tests/ApiTest.php
@@ -2,7 +2,9 @@
 
 require_once __DIR__ . "/../lessc.inc.php";
 
-class ApiTest extends PHPUnit_Framework_TestCase {
+use PHPUnit\Framework\TestCase;
+
+class ApiTest extends TestCase {
 	public function setUp() {
 		$this->less = new lessc();
 		$this->less->importDir = array(__DIR__ . "/inputs/test-imports");
diff --git a/tests/ErrorHandlingTest.php b/tests/ErrorHandlingTest.php
index f928974..5bb7b6f 100644
--- a/tests/ErrorHandlingTest.php
+++ b/tests/ErrorHandlingTest.php
@@ -1,7 +1,9 @@
 <?php
 require_once __DIR__ . "/../lessc.inc.php";
 
-class ErrorHandlingTest extends PHPUnit_Framework_TestCase {
+use PHPUnit\Framework\TestCase;
+
+class ErrorHandlingTest extends TestCase {
 	public function setUp() {
 		$this->less = new lessc();
 	}
diff --git a/tests/InputTest.php b/tests/InputTest.php
index 32db95b..8a0724c 100644
--- a/tests/InputTest.php
+++ b/tests/InputTest.php
@@ -2,6 +2,8 @@
 
 require_once __DIR__ . "/../lessc.inc.php";
 
+use PHPUnit\Framework\TestCase;
+
 // Runs all the tests in inputs/ and compares their output to ouputs/
 
 function _dump($value) {
@@ -12,7 +14,7 @@ function _quote($str) {
 	return preg_quote($str, "/");
 }
 
-class InputTest extends PHPUnit_Framework_TestCase {
+class InputTest extends TestCase {
 	protected static $importDirs = array("inputs/test-imports");
 
 	protected static $testDirs = array(
diff --git a/tests/ServerTest.php b/tests/ServerTest.php
index 5537f59..5e8a03f 100644
--- a/tests/ServerTest.php
+++ b/tests/ServerTest.php
@@ -1,6 +1,8 @@
 <?php
 
-class ServerTest extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+class ServerTest extends TestCase
 {
 
     public function testCheckedCachedCompile()