diff --git a/src/Configuration.php b/src/Configuration.php
index 467e197..aa1c76c 100644
--- a/src/Configuration.php
+++ b/src/Configuration.php
@@ -26,7 +26,7 @@ class Configuration
     /**
      * @var Mapper[]
      */
-    private $mappers;
+    private $mappers = [];
 
     /**
      * @param array              $config
diff --git a/tests/unit/ConfigurationTest.php b/tests/unit/ConfigurationTest.php
index 61dae9b..be8ed0c 100644
--- a/tests/unit/ConfigurationTest.php
+++ b/tests/unit/ConfigurationTest.php
@@ -129,7 +129,7 @@ public function mappingValues()
     /**
      * @test
      */
-    public function withPrefix()
+    public function withPrefixWithMappers()
     {
         $data = [
             'OUTER_PREFIX_ONE'   => 'One',
@@ -161,4 +161,19 @@ public function withPrefix()
 
         $sut->get('THING');
     }
+
+    /**
+     * @test
+     * @see https://github.com/improvframework/configuration/issues/7
+     */
+    public function withPrefixWithoutMappers()
+    {
+        $data = [ 'OUTER_PREFIX_ONE' => 'One' ];
+
+        // This call would raise an error as per:
+        //  https://github.com/improvframework/configuration/issues/7
+        $sut = (new Configuration($data, 'OUTER_'))->withPrefix('PREFIX_');
+
+        self::assertInstanceOf(Configuration::class, $sut);
+    }
 }