diff --git a/README.md b/README.md
index b653144e..9cf05dc7 100644
--- a/README.md
+++ b/README.md
@@ -134,6 +134,7 @@ to also theme standard elements, such as, button and textblock etc.
 
 
 - Removed the additional [ToolTip](https://github.com/Dirkster99/AvalonDock/commit/5554de5c4bfadc37f974ba29803dc792b54f00d0) and [ContextMenu](https://github.com/Dirkster99/AvalonDock/commit/103e1068bc9f5bae8fef275a0e785393b4115764) styles from the Generic.xaml in VS2013 [more details here](https://github.com/Dirkster99/AvalonDock/pull/170#issuecomment-674253874)
+- [#189 Removal of DictionaryTheme breaks my application](https://github.com/Dirkster99/AvalonDock/issues/189)  (thanx to [hamohn](https://github.com/hamohn))
 
 ## Fixes & Features added in Version 4.3
 
diff --git a/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs b/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs
index a1dffba6..0a36a813 100644
--- a/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs
+++ b/source/Components/AvalonDock/Controls/LayoutFloatingWindowControl.cs
@@ -1,4 +1,4 @@
-/************************************************************************
+/************************************************************************
    AvalonDock
 
    Copyright (C) 2007-2013 Xceed Software Inc.
@@ -36,7 +36,7 @@ namespace AvalonDock.Controls
 	public abstract class LayoutFloatingWindowControl : Window, ILayoutControl
 	{
 		#region fields
-
+		private ResourceDictionary currentThemeResourceDictionary; // = null
 		private bool _isInternalChange; //false
 		private readonly ILayoutElement _model;
 		private bool _attachDrag = false;
@@ -246,22 +246,40 @@ public double ContentMinWidth
 		#endregion Properties
 
 		#region Internal Methods
-
+		/// <summary>Is Invoked when AvalonDock's WPF Theme changes via the <see cref="DockingManager.OnThemeChanged()"/> method.</summary>
+		/// <param name="oldTheme"></param>
 		internal virtual void UpdateThemeResources(Theme oldTheme = null)
 		{
-			if (oldTheme != null)
+			if (oldTheme != null) // Remove the old theme if present
 			{
-				var resourceDictionaryToRemove =
-					Resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
-				if (resourceDictionaryToRemove != null)
-					Resources.MergedDictionaries.Remove(
-						resourceDictionaryToRemove);
+				if (oldTheme is DictionaryTheme)
+				{
+					if (currentThemeResourceDictionary != null)
+					{
+						Resources.MergedDictionaries.Remove(currentThemeResourceDictionary);
+						currentThemeResourceDictionary = null;
+					}
+				}
+				else
+				{
+					var resourceDictionaryToRemove =
+						Resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
+					if (resourceDictionaryToRemove != null)
+						Resources.MergedDictionaries.Remove(
+							resourceDictionaryToRemove);
+				}
 			}
 
+			// Implicit parameter to this method is the new theme already set here
 			var manager = _model.Root?.Manager;
 			if (manager?.Theme == null) return;
-
-			Resources.MergedDictionaries.Add(new ResourceDictionary { Source = manager.Theme.GetResourceUri() });
+			if (manager.Theme is DictionaryTheme dictionaryTheme)
+			{
+				currentThemeResourceDictionary = dictionaryTheme.ThemeResourceDictionary;
+				Resources.MergedDictionaries.Add(currentThemeResourceDictionary);
+			}
+			else
+				Resources.MergedDictionaries.Add(new ResourceDictionary { Source = manager.Theme.GetResourceUri() });
 		}
 
 		internal void AttachDrag(bool onActivated = true)
diff --git a/source/Components/AvalonDock/Controls/NavigatorWindow.cs b/source/Components/AvalonDock/Controls/NavigatorWindow.cs
index 8c808a7d..f488d12f 100644
--- a/source/Components/AvalonDock/Controls/NavigatorWindow.cs
+++ b/source/Components/AvalonDock/Controls/NavigatorWindow.cs
@@ -1,4 +1,4 @@
-/************************************************************************
+/************************************************************************
    AvalonDock
 
    Copyright (C) 2007-2013 Xceed Software Inc.
@@ -28,6 +28,7 @@ namespace AvalonDock.Controls
 	public class NavigatorWindow : Window
 	{
 		#region fields
+		private ResourceDictionary currentThemeResourceDictionary; // = null
 
 		private const string PART_AnchorableListBox = "PART_AnchorableListBox";
 		private const string PART_DocumentListBox = "PART_DocumentListBox";
@@ -286,17 +287,36 @@ protected override void OnPreviewKeyUp(System.Windows.Input.KeyEventArgs e)
 		/// <param name="value">The new value for the property.</param>
 		protected void SetDocuments(LayoutDocumentItem[] value) => SetValue(DocumentsPropertyKey, value);
 
+		/// <summary>Is Invoked when AvalonDock's WPF Theme changes via the <see cref="DockingManager.OnThemeChanged()"/> method.</summary>
+		/// <param name="oldTheme"></param>
 		internal void UpdateThemeResources(Theme oldTheme = null)
 		{
-			if (oldTheme != null)
+			if (oldTheme != null) // Remove the old theme if present
 			{
-				var resourceDictionaryToRemove = Resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
-				if (resourceDictionaryToRemove != null) Resources.MergedDictionaries.Remove(resourceDictionaryToRemove);
+				if (oldTheme is DictionaryTheme)
+				{
+					if (currentThemeResourceDictionary != null)
+					{
+						Resources.MergedDictionaries.Remove(currentThemeResourceDictionary);
+						currentThemeResourceDictionary = null;
+					}
+				}
+				else
+				{
+					var resourceDictionaryToRemove = Resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
+					if (resourceDictionaryToRemove != null) Resources.MergedDictionaries.Remove(resourceDictionaryToRemove);
+				}
 			}
 
+			// Implicit parameter to this method is the new theme already set here
 			if (_manager.Theme == null) return;
-
-			Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = _manager.Theme.GetResourceUri() });
+			if (_manager.Theme is DictionaryTheme dictionaryTheme)
+			{
+				currentThemeResourceDictionary = dictionaryTheme.ThemeResourceDictionary;
+				Resources.MergedDictionaries.Add(currentThemeResourceDictionary);
+			}
+			else
+				Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = _manager.Theme.GetResourceUri() });
 		}
 
 		internal void SelectNextDocument()
diff --git a/source/Components/AvalonDock/Controls/OverlayWindow.cs b/source/Components/AvalonDock/Controls/OverlayWindow.cs
index d5e64062..4ad7d5b4 100644
--- a/source/Components/AvalonDock/Controls/OverlayWindow.cs
+++ b/source/Components/AvalonDock/Controls/OverlayWindow.cs
@@ -1,4 +1,4 @@
-/************************************************************************
+/************************************************************************
    AvalonDock
 
    Copyright (C) 2007-2013 Xceed Software Inc.
@@ -25,6 +25,7 @@ namespace AvalonDock.Controls
 	public class OverlayWindow : Window, IOverlayWindow
 	{
 		#region fields
+		private ResourceDictionary currentThemeResourceDictionary; // = null
 
 		private Canvas _mainCanvasPanel;
 		private Grid _gridDockingManagerDropTargets;    // Showing and activating 4 outer drop taget buttons over DockingManager
@@ -169,21 +170,41 @@ protected override void OnClosing(System.ComponentModel.CancelEventArgs e)
 		#endregion Overrides
 
 		#region Internal Methods
-
+		/// <summary>Is Invoked when AvalonDock's WPF Theme changes via the <see cref="DockingManager.OnThemeChanged()"/> method.</summary>
+		/// <param name="oldTheme"></param>
 		internal void UpdateThemeResources(Theme oldTheme = null)
 		{
-			if (oldTheme != null)
+			if (oldTheme != null) // Remove the old theme if present
 			{
-				var resourceDictionaryToRemove =
-					Resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
-				if (resourceDictionaryToRemove != null)
-					Resources.MergedDictionaries.Remove(
-						resourceDictionaryToRemove);
+				if (oldTheme is DictionaryTheme)
+				{
+					if (currentThemeResourceDictionary != null)
+					{
+						Resources.MergedDictionaries.Remove(currentThemeResourceDictionary);
+						currentThemeResourceDictionary = null;
+					}
+				}
+				else
+				{
+					var resourceDictionaryToRemove =
+						Resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
+					if (resourceDictionaryToRemove != null)
+						Resources.MergedDictionaries.Remove(
+							resourceDictionaryToRemove);
+				}
 			}
 
-			if (_host.Manager.Theme != null)
+			if (_host.Manager.Theme != null) // Implicit parameter to this method is the new theme already set here
 			{
-				Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = _host.Manager.Theme.GetResourceUri() });
+				if (_host.Manager.Theme is DictionaryTheme theme)
+				{
+					currentThemeResourceDictionary = theme.ThemeResourceDictionary;
+					Resources.MergedDictionaries.Add(currentThemeResourceDictionary);
+				}
+				else
+				{
+					Resources.MergedDictionaries.Add(new ResourceDictionary() { Source = _host.Manager.Theme.GetResourceUri() });
+				}
 			}
 		}
 
diff --git a/source/Components/AvalonDock/DockingManager.cs b/source/Components/AvalonDock/DockingManager.cs
index 3909e684..f42c91fd 100644
--- a/source/Components/AvalonDock/DockingManager.cs
+++ b/source/Components/AvalonDock/DockingManager.cs
@@ -1,4 +1,4 @@
-/************************************************************************
+/************************************************************************
    AvalonDock
 
    Copyright (C) 2007-2013 Xceed Software Inc.
@@ -42,6 +42,9 @@ namespace AvalonDock
 	public class DockingManager : Control, IOverlayWindowHost//, ILogicalChildrenContainer
 	{
 		#region fields
+		// ShortCut to current AvalonDock theme if OnThemeChanged() is invoked with DictionaryTheme instance
+		// in e.OldValue and e.NewValue of the passed event
+		private ResourceDictionary currentThemeResourceDictionary;
 
 		private AutoHideWindowManager _autoHideWindowManager;
 		private FrameworkElement _autohideArea;
@@ -1029,24 +1032,41 @@ protected virtual void OnThemeChanged(DependencyPropertyChangedEventArgs e)
 		{
 			var oldTheme = e.OldValue as Theme;
 			var resources = Resources;
-			if (oldTheme != null)
+			if (oldTheme != null)        // remove old theme from resource dictionary if present
 			{
-				var resourceDictionaryToRemove =
-					resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
-				if (resourceDictionaryToRemove != null)
-					resources.MergedDictionaries.Remove(
-						resourceDictionaryToRemove);
+				if (oldTheme is DictionaryTheme)  // We are using AvalonDock's own DictionaryTheme class
+				{
+					if (currentThemeResourceDictionary != null)
+					{
+						resources.MergedDictionaries.Remove(currentThemeResourceDictionary);
+						currentThemeResourceDictionary = null;
+					}
+				}
+				else                              // We are using standard ResourceDictionaries
+				{                                // Lockup the old theme and remove it from resource dictionary
+					var resourceDictionaryToRemove =
+						resources.MergedDictionaries.FirstOrDefault(r => r.Source == oldTheme.GetResourceUri());
+					if (resourceDictionaryToRemove != null)
+						resources.MergedDictionaries.Remove(
+							resourceDictionaryToRemove);
+				}
 			}
 
-			if (e.NewValue as Theme != null)
+			if (e.NewValue as Theme != null) // Add new theme into resource dictionary if present
 			{
-				resources.MergedDictionaries.Add(new ResourceDictionary { Source = (e.NewValue as Theme).GetResourceUri() });
+				if (e.NewValue as Theme is DictionaryTheme theme)
+				{
+					currentThemeResourceDictionary = theme.ThemeResourceDictionary;
+					resources.MergedDictionaries.Add(currentThemeResourceDictionary);
+				}
+				else                              // We are using standard ResourceDictionaries -> Add new theme resource
+					resources.MergedDictionaries.Add(new ResourceDictionary { Source = (e.NewValue as Theme).GetResourceUri() });
 			}
 
-			foreach (var fwc in _fwList)
+			foreach (var fwc in _fwList)               // Update theme resources in floating window controls
 				fwc.UpdateThemeResources(oldTheme);
 
-			_navigatorWindow?.UpdateThemeResources();
+			_navigatorWindow?.UpdateThemeResources();  // Update theme resources in related AvalonDock controls
 			_overlayWindow?.UpdateThemeResources();
 		}
 
diff --git a/source/Components/AvalonDock/Themes/DictionaryTheme.cs b/source/Components/AvalonDock/Themes/DictionaryTheme.cs
new file mode 100644
index 00000000..fa8c5ac9
--- /dev/null
+++ b/source/Components/AvalonDock/Themes/DictionaryTheme.cs
@@ -0,0 +1,50 @@
+/************************************************************************
+   AvalonDock
+
+   Copyright (C) 2007-2013 Xceed Software Inc.
+
+   This program is provided to you under the terms of the Microsoft Public
+   License (Ms-PL) as published at https://opensource.org/licenses/MS-PL
+ ************************************************************************/
+
+using System;
+using System.Windows;
+
+namespace AvalonDock.Themes
+{
+	/// <summary>Defines a base class to implement a method for storing the current AvalonDock theme
+	/// that provides a XAML Uri pointing to a <see cref="ResourceDictionary"/>.
+	/// 
+	/// This class can be used to create customized themes by loading a <see cref="ResourceDictionary"/>
+	/// from an existing theme (by using theme.GetResourceUri()), and then replacing some key colors
+	/// (typically the "Accent" colors).
+	/// 
+	/// See Issue https://github.com/Dirkster99/AvalonDock/issues/189 for more details.</summary>
+	public abstract class DictionaryTheme : Theme
+	{
+		#region Constructors
+		/// <summary>Class constructor</summary>
+		public DictionaryTheme()
+		{
+		}
+
+		/// <summary>Class constructor from theme specific resource dictionary.</summary>
+		/// <param name="themeResourceDictionary"></param>
+		public DictionaryTheme(ResourceDictionary themeResourceDictionary)
+		{
+			this.ThemeResourceDictionary = themeResourceDictionary;
+		}
+
+		#endregion Constructors
+
+		/// <summary>Gets the resource dictionary that is associated with this AvalonDock theme.</summary>
+		public ResourceDictionary ThemeResourceDictionary { get; private set; }
+
+		/// <summary>Gets the <see cref="Uri"/> of the XAML that contains the definition for this AvalonDock theme.</summary>
+		/// <returns><see cref="Uri"/> of the XAML that contains the definition for this custom AvalonDock theme</returns>
+		public override Uri GetResourceUri()
+		{
+			return null;
+		}
+	}
+}