diff --git a/lib/fast_transformer.d.ts b/lib/fast_transformer.d.ts
index e63b30e..8dd784a 100644
--- a/lib/fast_transformer.d.ts
+++ b/lib/fast_transformer.d.ts
@@ -17,6 +17,12 @@ export class FastTransformer implements Transformer {
 	 */
 	close(): Promise<void>;
 
+	/**
+	 * Starts the underlying PHP process and begins accepting connections.
+	 * @returns The TCP port used by the PHP process.
+	 */
+	listen(): Promise<number>;
+
 	/**
 	 * Processes a PHP script.
 	 * @param file The path to the PHP script.