diff --git a/src/register.ts b/src/register.ts
index 929b7a0..1299a64 100644
--- a/src/register.ts
+++ b/src/register.ts
@@ -45,13 +45,20 @@ function getCoreModules(
   return coreModules;
 }
 
+export interface RegisterParams extends ExplicitParams {
+  /**
+   * Defaults to `--project` CLI flag or `process.cwd()`
+   */
+  cwd?: string;
+}
+
 /**
  * Installs a custom module load function that can adhere to paths in tsconfig.
  * Returns a function to undo paths registration.
  */
-export function register(explicitParams: ExplicitParams): () => void {
+export function register(explicitParams?: RegisterParams): () => void {
   const configLoaderResult = configLoader({
-    cwd: options.cwd,
+    cwd: explicitParams?.cwd ?? options.cwd,
     explicitParams,
   });