diff --git a/project.json b/project.json
index f6ee0e6..5424afe 100644
--- a/project.json
+++ b/project.json
@@ -35,7 +35,7 @@
         "company": "Nosial",
         "copyright": "Copyright (c) 2022-2023 Nosial",
         "description": "ConfigLib is a library for reading and writing configuration files via the NCC Runtime API",
-        "version": "1.1.0",
+        "version": "1.1.1",
         "uuid": "9347259e-8e4d-11ed-85a7-fd07cf28ef35"
     },
     "build": {
diff --git a/src/ConfigLib/Configuration.php b/src/ConfigLib/Configuration.php
index 86ee637..62b604a 100644
--- a/src/ConfigLib/Configuration.php
+++ b/src/ConfigLib/Configuration.php
@@ -161,9 +161,7 @@
          */
         private static function validateKey(string $input): bool
         {
-            $pattern = '/^([a-zA-Z0-9]+\.?)+$/';
-
-            if (preg_match($pattern, $input))
+            if (preg_match('/^([a-zA-Z0-9_]+\.?)+$/', $input))
             {
                 return true;
             }
diff --git a/tests/ConfigLib/ConfigurationTest.php b/tests/ConfigLib/ConfigurationTest.php
index a657551..2f8330b 100644
--- a/tests/ConfigLib/ConfigurationTest.php
+++ b/tests/ConfigLib/ConfigurationTest.php
@@ -52,8 +52,10 @@ class ConfigurationTest extends TestCase
     public function testGetMethodWithValidKey(): void
     {
         $config = new Configuration('test');
-        $config->set('key1.key2', 'value');
+        $this->assertTrue($config->set('key1.key2', 'value', true));
         $this->assertEquals('value', $config->get('key1.key2'));
+        $this->assertTrue($config->set('foo.fizz_buzz', 'value', true));
+        $this->assertEquals('value', $config->get('foo.fizz_buzz'));
     }
 
     /**