diff --git a/.travis.yml b/.travis.yml
index 1f9c60f..06dba43 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,5 @@
 language: php
 php:
-  - '5.4'
   - '5.5'
   - '5.6'
   - '7.0'
@@ -9,7 +8,9 @@ php:
   - nightly
 
 before_script:
+  sudo apt-get install p7zip-full -y
+  sudo apt-get install zipalign -y
   composer install
 
 script:
-  vendor/bin/phpunit -v -c bootstrap.xml
\ No newline at end of file
+  vendor/bin/phpunit -v --tap -c bootstrap.xml
\ No newline at end of file
diff --git a/README.md b/README.md
index 1a62197..2067f9b 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,7 @@ Features:
 
 Requirements
 ------------
-- `PHP` >= 5.4 (64 bit)
+- `PHP` >= 5.5 (64 bit)
 - PHP-extension `mbstring`
 - Optional php-extension `bzip2` for BZIP2 compression.
 - Optional php-extension `openssl` or `mcrypt` for `WinZip Aes Encryption` support.
diff --git a/composer.json b/composer.json
index 1f37110..2b8d2ac 100644
--- a/composer.json
+++ b/composer.json
@@ -23,7 +23,7 @@
   ],
   "minimum-stability": "stable",
   "require": {
-    "php-64bit": "^5.4 || ^7.0"
+    "php-64bit": "^5.5 || ^7.0"
   },
   "autoload": {
     "psr-4": {
diff --git a/src/PhpZip/Extra/ExtraField.php b/src/PhpZip/Extra/ExtraField.php
index a95c519..7872660 100644
--- a/src/PhpZip/Extra/ExtraField.php
+++ b/src/PhpZip/Extra/ExtraField.php
@@ -62,8 +62,8 @@ abstract class ExtraField implements ExtraFieldHeader
     private static function getRegistry()
     {
         if (self::$registry === null) {
-            self::$registry[WinZipAesEntryExtraField::getHeaderId()] = '\PhpZip\Extra\WinZipAesEntryExtraField';
-            self::$registry[NtfsExtraField::getHeaderId()] = '\PhpZip\Extra\NtfsExtraField';
+            self::$registry[WinZipAesEntryExtraField::getHeaderId()] = WinZipAesEntryExtraField::class;
+            self::$registry[NtfsExtraField::getHeaderId()] = NtfsExtraField::class;
         }
         return self::$registry;
     }