diff --git a/Windows/VideoFrameAnalyzer/FrameGrabber.cs b/Windows/VideoFrameAnalyzer/FrameGrabber.cs
index 0c3dbf2..194d893 100644
--- a/Windows/VideoFrameAnalyzer/FrameGrabber.cs
+++ b/Windows/VideoFrameAnalyzer/FrameGrabber.cs
@@ -128,8 +128,8 @@ namespace VideoFrameAnalyzer
         protected Predicate<VideoFrame> _analysisPredicate = null;
         protected VideoCapture _reader = null;
         protected Timer _timer = null;
-        protected readonly SemaphoreSlim _timerMutex = new SemaphoreSlim(1);
-        protected readonly AutoResetEvent _frameGrabTimer = new AutoResetEvent(false);
+        protected SemaphoreSlim _timerMutex = new SemaphoreSlim(1);
+        protected AutoResetEvent _frameGrabTimer = new AutoResetEvent(false);
         protected bool _stopping = false;
         protected Task _producerTask = null;
         protected Task _consumerTask = null;