diff --git a/packages/jspsych/src/modules/plugin-api/MediaAPI.ts b/packages/jspsych/src/modules/plugin-api/MediaAPI.ts
index 27868fe1..c94a8f2b 100644
--- a/packages/jspsych/src/modules/plugin-api/MediaAPI.ts
+++ b/packages/jspsych/src/modules/plugin-api/MediaAPI.ts
@@ -324,7 +324,7 @@ export class MediaAPI {
     this.preload_requests = [];
   }
 
-  private microphone_recorder: MediaRecorder;
+  private microphone_recorder: MediaRecorder = null;
 
   initializeMicrophoneRecorder(stream: MediaStream) {
     const recorder = new MediaRecorder(stream);