diff --git a/.travis.yml b/.travis.yml
index 480b369..b3ec074 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -13,8 +13,7 @@ matrix:
     include:
 
         # install vendor packages with lowest version
-#        - php: 5.4
-#          env: COMPOSER_ARGS="--prefer-lowest"
+        - php: 5.6
 
         # install vendor packages with newest version and run Codeception with coverage
         - php: 7.1
diff --git a/composer.json b/composer.json
index 7c71f23..a645076 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,7 @@
     ],
     "require": {
         "maba/dependency-injection-extra": "^0.1.1",
-        "php": ">=7.0",
+        "php": ">=5.6",
         "satooshi/php-coveralls": "^1.0",
         "symfony/console": "^2.5|^3.0",
         "symfony/dependency-injection": "^2.6|^3.0",
diff --git a/src/Service/AssetManager.php b/src/Service/AssetManager.php
index 8dcfd82..c4cd98a 100644
--- a/src/Service/AssetManager.php
+++ b/src/Service/AssetManager.php
@@ -113,8 +113,11 @@ private function getManifestEntry($assetName, $exceptionInfo)
 
 		if (!isset($this->manifest[$assetName])) {
 
-			$assetDescription = $exceptionInfo['assetDescription'] ?? "'$assetName'";
-			$errorDescription = ($exceptionInfo['errorDescription'] ?? '') . ' Is webpack:dev-server running in the background?';
+			$assetDescription = isset($exceptionInfo['assetDescription']) ? $exceptionInfo['assetDescription'] : "'$assetName'";
+
+			$errorDescription = (isset($exceptionInfo['errorDescription']) ? $exceptionInfo['errorDescription'] : '')
+				. ' Is webpack:dev-server running in the background?'
+			;
 
 			throw new RuntimeException(
 				sprintf('No information in manifest for %s. %s', $assetDescription, trim($errorDescription))
diff --git a/src/Webpack/Config/WebpackConfigManager.php b/src/Webpack/Config/WebpackConfigManager.php
index 256468e..166c87b 100644
--- a/src/Webpack/Config/WebpackConfigManager.php
+++ b/src/Webpack/Config/WebpackConfigManager.php
@@ -27,7 +27,7 @@ public function __construct(
 		AliasProvider $aliasProvider,
 		AssetCollector $assetCollector,
 		WebpackConfigDumper $configDumper,
-		string $configPath,
+		$configPath,
 		AssetResolver $assetResolver,
 		AssetNameGenerator $assetNameGenerator,
 		ErrorHandlerInterface $errorHandler