diff --git a/Source/FileManager/ReplacementCharacters.cs b/Source/FileManager/ReplacementCharacters.cs
index ed2422da..476299fb 100644
--- a/Source/FileManager/ReplacementCharacters.cs
+++ b/Source/FileManager/ReplacementCharacters.cs
@@ -154,14 +154,18 @@ namespace FileManager
 					Replacement.OtherQuote("\"")]
 		};
 		#endregion
+		/// <summary>
+		/// Characters to consider invalid in filenames in addition to those returned by <see cref="Path.GetInvalidFileNameChars()"/>
+		/// </summary>
+		public static char[] AdditionalInvalidFilenameCharacters { get; set; } = [];
 
 		internal static bool IsWindows => Environment.OSVersion.Platform is PlatformID.Win32NT;
 
-		private static readonly char[] invalidPathChars = Path.GetInvalidFileNameChars().Except(new[] {
+		private static char[] invalidPathChars { get; } = Path.GetInvalidFileNameChars().Except(new[] {
 				Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar
 			}).ToArray();
 
-		private static readonly char[] invalidSlashes = Path.GetInvalidFileNameChars().Intersect(new[] {
+		private static char[] invalidSlashes { get; } = Path.GetInvalidFileNameChars().Intersect(new[] {
 				Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar
 			}).ToArray();
 
@@ -220,8 +224,11 @@ namespace FileManager
 			return DefaultReplacement;
 		}
 
+		private static bool CharIsPathInvalid(char c)
+			=> invalidPathChars.Contains(c) || AdditionalInvalidFilenameCharacters.Contains(c);
+
 		public static bool ContainsInvalidPathChar(string path)
-			=> path.Any(c => invalidPathChars.Contains(c));
+			=> path.Any(CharIsPathInvalid);
 		public static bool ContainsInvalidFilenameChar(string path)
 			=> ContainsInvalidPathChar(path) || path.Any(c => invalidSlashes.Contains(c));
 
@@ -233,7 +240,7 @@ namespace FileManager
 			{
 				var c = fileName[i];
 
-				if (invalidPathChars.Contains(c)
+				if (CharIsPathInvalid(c)
 					|| invalidSlashes.Contains(c)
 					|| Replacements.Any(r => r.CharacterToReplace == c) /* Replace any other legal characters that they user wants. */ )
 				{
@@ -258,14 +265,14 @@ namespace FileManager
 
 				if (
 					(
-						invalidPathChars.Contains(c)
-						|| (	// Replace any other legal characters that they user wants.
+						CharIsPathInvalid(c)
+						|| (    // Replace any other legal characters that they user wants.
 								c != Path.DirectorySeparatorChar
 								&& c != Path.AltDirectorySeparatorChar
 								&& Replacements.Any(r => r.CharacterToReplace == c)
 							)
 					)
-					&& !(	// replace all colons except drive letter designator on Windows
+					&& !(   // replace all colons except drive letter designator on Windows
 							c == ':'
 							&& i == 1
 							&& Path.IsPathRooted(pathStr)
@@ -273,9 +280,9 @@ namespace FileManager
 					)
 				)
 				{
-						char preceding = i > 0 ? pathStr[i - 1] : default;
-						char succeeding = i < pathStr.Length - 1 ? pathStr[i + 1] : default;
-						builder.Append(GetPathCharReplacement(c, preceding, succeeding));
+					char preceding = i > 0 ? pathStr[i - 1] : default;
+					char succeeding = i < pathStr.Length - 1 ? pathStr[i + 1] : default;
+					builder.Append(GetPathCharReplacement(c, preceding, succeeding));
 				}
 				else
 					builder.Append(c);
diff --git a/Source/LibationAvalonia/Views/MainWindow.axaml.cs b/Source/LibationAvalonia/Views/MainWindow.axaml.cs
index f1bb1a28..bf7c4853 100644
--- a/Source/LibationAvalonia/Views/MainWindow.axaml.cs
+++ b/Source/LibationAvalonia/Views/MainWindow.axaml.cs
@@ -51,29 +51,13 @@ namespace LibationAvalonia.Views
 		[Dinah.Core.PropertyChangeFilter(nameof(Configuration.Books))]
 		private void Settings_PropertyChanged(object sender, Dinah.Core.PropertyChangedEventArgsEx e)
 		{
-			if (!Configuration.IsWindows && !Configuration.Instance.BooksCanWriteWindowsInvalidChars)
+			if (!Configuration.IsWindows)
 			{
 				//The books directory does not support filenames with windows' invalid characters.
-				//Ensure that the ReplacementCharacters configuration has replacements for all invalid characters.
-				//We can't rely on the "other invalid characters" replacement because that is only used by
-				//ReplacementCharacters for platform-specific illegal characters, whereas for the Books directory
-				//we are concerned with the ultimate destination directory's capabilities. 
-				var defaults = ReplacementCharacters.Default(true).Replacements;
-				var replacements = Configuration.Instance.ReplacementCharacters.Replacements.ToList();
-				bool changed = false;
-				foreach (var c in FileSystemTest.AdditionalInvalidWindowsFilenameCharacters)
-				{
-					if (!replacements.Any(r => r.CharacterToReplace == c))
-					{
-						var replacement = defaults.FirstOrDefault(r => r.CharacterToReplace == c) ?? defaults[0];
-						replacements.Add(replacement);
-						changed = true;
-					}
-				}
-				if (changed)
-				{
-					Configuration.Instance.ReplacementCharacters = new ReplacementCharacters { Replacements = replacements };
-				}
+				//Tell the ReplacementCharacters configuration to treat those characters as invalid.
+				ReplacementCharacters.AdditionalInvalidFilenameCharacters
+					= Configuration.Instance.BooksCanWriteWindowsInvalidChars ? []
+					: FileSystemTest.AdditionalInvalidWindowsFilenameCharacters.ToArray();
 			}
 		}
 
@@ -161,7 +145,7 @@ namespace LibationAvalonia.Views
 				Configuration.Instance.FirstLaunch = false;
 			}
 		}
-		
+
 		private void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
 		{
 			productsDisplay?.CloseImageDisplay();