diff --git a/.travis.yml b/.travis.yml
index 7c505dc..4df3e48 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,14 +2,9 @@ language: php
 
 matrix:
     include:
-        - php: 5.3
-          dist: precise
-        - php: 5.4
-        - php: 5.5
-        - php: 5.6
-        - php: 7.0
         - php: 7.1
         - php: 7.2
+        - php: 7.3
         - php: nightly
     fast_finish: true
     allow_failures:
@@ -17,15 +12,13 @@ matrix:
 
 before_install:
     - phpenv config-rm xdebug.ini || true
-    - composer config --global github-oauth.github.com $GITHUB_TOKEN
-install: composer install --prefer-dist --no-progress --no-interaction
+install: composer install --no-progress --no-interaction
 script: scripts/travis
 after_script: scripts/travis-after
 
 env:
     global:
         - ELOQUENT_PUBLISH_VERSION=7.1
-        - secure: "kK6XSHAaOLavtUZthJr3+VpsCedSrf0eJXz+lit/i2weg8g7RrReo2Ta/pWhzS3aP6mHkRKyB4UzMVebuFOoHuJkn+WGgnVUp1YhmL9F9wK4rzJQlGDmcwpSI3v6G69Mzm10o1v4ZVtAlaDD7MzbkTC8bw/Vg2BYeRZ8jFCzI7U="
 
 cache:
     directories:
diff --git a/composer.json b/composer.json
index 1e66c91..9ffd0be 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3"
+        "php": ">=7.1"
     },
     "require-dev": {
         "phpunit/phpunit": "^4"
@@ -27,7 +27,7 @@
     },
     "config": {
         "platform": {
-            "php": "5.3.99"
+            "php": "7.1.99"
         }
     }
 }
diff --git a/src/AbstractEnumeration.php b/src/AbstractEnumeration.php
index 7838be7..a2637f7 100644
--- a/src/AbstractEnumeration.php
+++ b/src/AbstractEnumeration.php
@@ -23,8 +23,10 @@ final protected static function initializeMembers()
     {
         $reflector = new ReflectionClass(get_called_class());
 
-        foreach ($reflector->getConstants() as $key => $value) {
-            new static($key, $value);
+        foreach ($reflector->getReflectionConstants() as $constant) {
+            if ($constant->isPublic()) {
+                new static($constant->getName(), $constant->getValue());
+            }
         }
     }
 }
diff --git a/test/src/MixedAccessibilityEnumeration.php b/test/src/MixedAccessibilityEnumeration.php
new file mode 100644
index 0000000..b6900a4
--- /dev/null
+++ b/test/src/MixedAccessibilityEnumeration.php
@@ -0,0 +1,17 @@
+<?php
+
+use Eloquent\Enumeration\AbstractEnumeration;
+
+/**
+ * An enumeration whose members have different accessibility levels.
+ *
+ * @method static IMPLICIT_PUBLIC()
+ * @method static EXPLICIT_PUBLIC()
+ */
+final class MixedAccessibilityEnumeration extends AbstractEnumeration
+{
+    const IMPLICIT_PUBLIC = 'IMPLICIT_PUBLIC';
+    public const EXPLICIT_PUBLIC = 'EXPLICIT_PUBLIC';
+    protected const PROTECTED = 'PROTECTED';
+    private const PRIVATE = 'PRIVATE';
+}
diff --git a/test/suite/FunctionalTest.php b/test/suite/FunctionalTest.php
index 3ca972c..2667e21 100644
--- a/test/suite/FunctionalTest.php
+++ b/test/suite/FunctionalTest.php
@@ -120,4 +120,16 @@ public function testPlanetExampleScriptOutput()
 
         $this->assertSame($expected, $actual);
     }
+
+    /**
+     * Tests that only public constants are included as enumeration members.
+     */
+    public function testMixedAccessibility()
+    {
+        $members = MixedAccessibilityEnumeration::members();
+
+        self::assertCount(2, $members);
+        self::assertArrayHasKey(MixedAccessibilityEnumeration::IMPLICIT_PUBLIC, $members);
+        self::assertArrayHasKey(MixedAccessibilityEnumeration::EXPLICIT_PUBLIC, $members);
+    }
 }