diff --git a/features/server.feature b/features/server.feature
index badb0f2..ba3f573 100644
--- a/features/server.feature
+++ b/features/server.feature
@@ -32,6 +32,24 @@ Feature: Serve WordPress locally
       256M
       """
 
+  Scenario: Custom ini configuration
+    Given a WP install
+    And a mem.php file:
+      """
+      <?php echo ini_get('memory_limit'); ?>
+      """
+    And a custom.ini file:
+      """
+      memory_limit = 512M
+      """
+    And I launch in the background `wp server --host=localhost --port=8188 --config=custom.ini`
+
+    When I run `curl -sS localhost:8188/mem.php`
+    Then STDOUT should be:
+      """
+      512M
+      """
+
   Scenario: Access wp-login.php
     Given a WP install
     And I launch in the background `wp server --host=localhost --port=8185`
diff --git a/src/Server_Command.php b/src/Server_Command.php
index 1e33023..0faa860 100644
--- a/src/Server_Command.php
+++ b/src/Server_Command.php
@@ -125,17 +125,23 @@ public function __invoke( $args, $assoc_args ) {
 		}
 
 		// Add the server flags
-		$cmd_format .= ' -S %s -t %s -c %s %s';
+		$cmd_format .= ' -S %s -t %s';
 		$cmd_args[]  = $assoc_args['host'] . ':' . $assoc_args['port'];
-		$cmd_args[]  = $docroot;
-		$cmd_args[]  = $assoc_args['config'];
+		$cmd_args[]  = (string) $docroot;
+
+		if ( ! empty( $assoc_args['config'] ) && is_string( $assoc_args['config'] ) ) {
+			$cmd_format .= ' -c %s';
+			$cmd_args[]  = $assoc_args['config'];
+		}
+
+		$cmd_format .= ' %s';
 		$cmd_args[]  = Utils\extract_from_phar( $router_path );
 
 		$cmd = Utils\esc_cmd( $cmd_format, ...$cmd_args );
 
 		$descriptors = array( STDIN, STDOUT, STDERR );
 
-		if ( Utils\get_flag_value( $assoc_args, 'adapt-scheme', false ) ) { // @phpstan-ignore argument.type
+		if ( Utils\get_flag_value( $assoc_args, 'adapt-scheme', false ) ) {
 			putenv( 'WPCLI_SERVER_ADAPT_SCHEME=1' );
 		}