diff --git a/CHANGELOG.md b/CHANGELOG.md
index b48481a..0791789 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@
   * Add `database.extra_databases`
   * Add `php.phpstan.baseline` as an optional boolean.
   * Add `node.version` as a string.
+* Add a test to ensure extra databases is an optional array of non-blank strings.
 * Add a test to ensure the project type is a valid type.
 * Add a test to ensure the web server is a valid type.
 * Add a `test` task to `run` script.
diff --git a/src/DataTransferObject/Config.php b/src/DataTransferObject/Config.php
index 3d562d0..f47b05f 100644
--- a/src/DataTransferObject/Config.php
+++ b/src/DataTransferObject/Config.php
@@ -16,6 +16,7 @@ final class Config
             'extra_databases' => new Assert\Optional([
                 new Assert\Type('array'),
                 new Assert\All([
+                    new Assert\NotBlank(),
                     new Assert\Type('string'),
                 ]),
             ]),
diff --git a/tests/Kernel/Validator/ConfigurationValidatorTest.php b/tests/Kernel/Validator/ConfigurationValidatorTest.php
index 8c8ab01..c4be1be 100644
--- a/tests/Kernel/Validator/ConfigurationValidatorTest.php
+++ b/tests/Kernel/Validator/ConfigurationValidatorTest.php
@@ -12,15 +12,54 @@ use Symfony\Component\Validator\Validator\ValidatorInterface;
 
 class ConfigurationValidatorTest extends KernelTestCase
 {
+    private Config $configurationDataDTO;
+
     private ValidatorInterface $validator;
 
     public function setUp(): void
     {
+        $this->configurationDataDTO = self::createConfigurationDTO();
+
         $this->validator = Validation::createValidatorBuilder()
             ->enableAnnotationMapping()
             ->getValidator();
     }
 
+    /**
+     * @dataProvider extraDatabaseProvider
+     */
+    public function testThatExtraDatabasesCanBeSpecified(
+        ?array $extraDatabases,
+        int $expectedViolationCount,
+        ?string $expectedMessage,
+    ): void
+    {
+        $this->configurationDataDTO->database = [
+            'extra_databases' => $extraDatabases,
+            'type' => 'mariadb',
+            'version' => 10,
+        ];
+
+        $violations = $this->validator->validate($this->configurationDataDTO);
+
+        self::assertCount(
+            expectedCount: $expectedViolationCount,
+            haystack: $violations,
+        );
+
+        if ($expectedViolationCount > 0) {
+            self::assertSame(
+                actual: 'database[extra_databases][0]',
+                expected: $violations[0]->getPropertyPath(),
+            );
+
+            self::assertSame(
+                actual: $expectedMessage,
+                expected: $violations[0]->getMessage(),
+            );
+        }
+    }
+
     /**
      * @dataProvider projectNameProvider
      */
@@ -118,6 +157,16 @@ class ConfigurationValidatorTest extends KernelTestCase
         }
     }
 
+    public function extraDatabaseProvider(): \Generator
+    {
+        return [
+            yield 'correct' => [['migrate'], 0, null],
+            yield 'empty string' => [[''], 1, 'This value should not be blank.'],
+            yield 'missing' => [null, 0, null],
+            yield 'no extra databases' => [[], 0, null],
+        ];
+    }
+
     public function projectLanguageProvider(): \Generator
     {
         return [