diff --git a/src/act/act.ts b/src/act/act.ts
index f489758..6735bb2 100644
--- a/src/act/act.ts
+++ b/src/act/act.ts
@@ -300,10 +300,10 @@ export class Act {
     }
 
     if (opts?.artifactServer) {
-      actArguments.push(
-        "--artifact-server-path", opts?.artifactServer.path,
-        "--artifact-server-port", opts?.artifactServer.port
-      );
+      actArguments.push("--artifact-server-path", opts?.artifactServer.path);
+      if (opts.artifactServer.port) {
+        actArguments.push("--artifact-server-port", opts?.artifactServer.port);
+      }
     }
 
     if (opts?.bind) {
diff --git a/src/act/act.type.ts b/src/act/act.type.ts
index 14f0180..6fbc907 100644
--- a/src/act/act.type.ts
+++ b/src/act/act.type.ts
@@ -27,7 +27,7 @@ export type RunOpts = {
   workflowFile?: string;
   artifactServer?: {
     path: string;
-    port: string;
+    port?: string;
   };
   mockApi?: ResponseMocker<unknown, number>[];
   mockSteps?: MockStep;