diff --git a/Pixiview/Illust/IllustCollectionPage.cs b/Pixiview/Illust/IllustCollectionPage.cs
index e1bf2cd..6be9cb3 100644
--- a/Pixiview/Illust/IllustCollectionPage.cs
+++ b/Pixiview/Illust/IllustCollectionPage.cs
@@ -504,7 +504,7 @@ namespace Pixiview.Illust
     public abstract class IllustScrollableCollectionPage<T> : IllustCollectionPage<T>
     {
         protected const int SCROLL_OFFSET = 33;
-        protected static readonly object sync = new object();
+        protected readonly object sync = new object();
 
         private double lastScrollY = double.MinValue;
         private double offset;
diff --git a/Pixiview/Illust/ViewIllustPage.xaml.cs b/Pixiview/Illust/ViewIllustPage.xaml.cs
index 26a5683..5fd0a75 100644
--- a/Pixiview/Illust/ViewIllustPage.xaml.cs
+++ b/Pixiview/Illust/ViewIllustPage.xaml.cs
@@ -153,8 +153,10 @@ namespace Pixiview.Illust
 
             if (ugoira != null)
             {
-                ugoira.TogglePlay(false);
                 IllustItem.IsPlaying = false;
+                ugoira.TogglePlay(false);
+                ugoira.Dispose();
+                ugoira = null;
             }
 
             if (saveFavorites)
diff --git a/Pixiview/Utils/HttpUtility.cs b/Pixiview/Utils/HttpUtility.cs
index 3040a5b..be7507b 100644
--- a/Pixiview/Utils/HttpUtility.cs
+++ b/Pixiview/Utils/HttpUtility.cs
@@ -292,8 +292,10 @@ namespace Pixiview.Utils
         }
     }
 
-    public class Ugoira
+    public class Ugoira : IDisposable
     {
+        private readonly object sync = new object();
+
         private readonly IllustUgoiraBody ugoira;
         private readonly IllustDetailItem detailItem;
         private readonly ImageSource[] frames;
@@ -315,21 +317,39 @@ namespace Pixiview.Utils
             Task.Run(LoadFrames);
         }
 
+        public void Dispose()
+        {
+            lock (sync)
+            {
+                if (IsPlaying)
+                {
+                    TogglePlay(false);
+                }
+            }
+            if (timer != null)
+            {
+                timer.Dispose();
+            }
+        }
+
         public void TogglePlay(bool flag)
         {
-            if (IsPlaying == flag)
+            lock (sync)
             {
-                return;
-            }
-            if (flag)
-            {
-                IsPlaying = true;
-                timer.Change(0, Timeout.Infinite);
-            }
-            else
-            {
-                IsPlaying = false;
-                timer.Change(Timeout.Infinite, Timeout.Infinite);
+                if (IsPlaying == flag)
+                {
+                    return;
+                }
+                if (flag)
+                {
+                    IsPlaying = true;
+                    timer.Change(0, Timeout.Infinite);
+                }
+                else
+                {
+                    IsPlaying = false;
+                    timer.Change(Timeout.Infinite, Timeout.Infinite);
+                }
             }
         }
 
@@ -359,9 +379,12 @@ namespace Pixiview.Utils
 
         private void OnTimerCallback(object state)
         {
-            if (!IsPlaying)
+            lock (sync)
             {
-                return;
+                if (!IsPlaying)
+                {
+                    return;
+                }
             }
 
             ImageSource frame;
@@ -384,7 +407,13 @@ namespace Pixiview.Utils
                 i = 0;
             }
             index = i;
-            timer.Change(info.delay, Timeout.Infinite);
+            lock (sync)
+            {
+                if (IsPlaying)
+                {
+                    timer.Change(info.delay, Timeout.Infinite);
+                }
+            }
         }
 
         private const int BUFFER_SIZE = 300000;