diff --git a/.gitignore b/.gitignore
index 6441b88..675a234 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,5 +3,5 @@
 .idea
 /vendor/
 /composer.lock
-
+.phpunit.result.cache
 *.swp
diff --git a/.travis.yml b/.travis.yml
index d07c55d..d704962 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,10 @@
 language: php
 
 php:
-  - 5.6
-  - 7.0
-  - 7.1
-  - 7.2
+  - 7.3
+  - 7.4
+  - 8.0
+  - nightly
 
 cache:
   directories:
@@ -20,5 +20,5 @@ script:
 
   # Execute PHPUnit tests
   - composer install --prefer-dist
-  - vendor/bin/phpunit --coverage-text
+  - XDEBUG_MODE=coverage vendor/bin/phpunit --coverage-text
   - composer lint
diff --git a/README.md b/README.md
index 1308ab9..faaa1b5 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@
 
 This is an extremely simple PHP [DogStatsD](https://docs.datadoghq.com/developers/dogstatsd/?tab=php) client.
 
-**Requires PHP >= 5.6.0.**
+**Requires PHP >= 7.3.0.**
 
 See [CHANGELOG.md](CHANGELOG.md) for changes.
 
diff --git a/composer.json b/composer.json
index 0879208..9cd6950 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,7 @@
         }
     ],
     "require": {
-        "php": ">=5.6.0",
+        "php": ">=7.3.0",
         "ext-curl": "*",
         "lib-curl": "*",
         "ext-sockets": "*"
@@ -49,7 +49,7 @@
         "sort-packages": true
     },
     "require-dev": {
-        "phpunit/phpunit": "5.7.27",
+        "phpunit/phpunit": "8.5.15",
         "squizlabs/php_codesniffer": "^3.3"
     },
     "scripts": {
diff --git a/tests/TestHelpers/CurlSpyTestCase.php b/tests/TestHelpers/CurlSpyTestCase.php
index 050afcf..7ec23fc 100644
--- a/tests/TestHelpers/CurlSpyTestCase.php
+++ b/tests/TestHelpers/CurlSpyTestCase.php
@@ -11,7 +11,7 @@ class CurlSpyTestCase extends TestCase
     /**
      * Set up a spy object to capture calls to built in curl functions
      */
-    protected function setUp()
+    protected function setUp(): void
     {
         global $curlSpy;
 
diff --git a/tests/TestHelpers/SocketSpyTestCase.php b/tests/TestHelpers/SocketSpyTestCase.php
index 24b1514..8d38d6c 100644
--- a/tests/TestHelpers/SocketSpyTestCase.php
+++ b/tests/TestHelpers/SocketSpyTestCase.php
@@ -24,7 +24,7 @@ class SocketSpyTestCase extends TestCase
     /**
      * Set up a spy object to capture calls to global built in socket functions
      */
-    protected function setUp()
+    protected function setUp(): void
     {
         global $socketSpy;
 
diff --git a/tests/UnitTests/BatchedDogStatsdTest.php b/tests/UnitTests/BatchedDogStatsdTest.php
index ae707de..971e2b5 100644
--- a/tests/UnitTests/BatchedDogStatsdTest.php
+++ b/tests/UnitTests/BatchedDogStatsdTest.php
@@ -8,7 +8,7 @@
 
 class BatchedDogStatsdTest extends SocketSpyTestCase
 {
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
 
diff --git a/tests/UnitTests/DogStatsd/SocketsTest.php b/tests/UnitTests/DogStatsd/SocketsTest.php
index 7163884..da1dbfc 100644
--- a/tests/UnitTests/DogStatsd/SocketsTest.php
+++ b/tests/UnitTests/DogStatsd/SocketsTest.php
@@ -9,7 +9,7 @@
 
 class SocketsTest extends SocketSpyTestCase
 {
-    public function setUp()
+    public function setUp(): void
     {
         parent::setUp();