diff --git a/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/Speller.cs b/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/Speller.cs
index 56e3b5b7255..3aceff72a9a 100644
--- a/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/Speller.cs
+++ b/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/Speller.cs
@@ -53,6 +53,7 @@ internal Speller(TextEditor textEditor)
 
             _defaultCulture = InputLanguageManager.Current != null ? InputLanguageManager.Current.CurrentInputLanguage :
                                                                      Thread.CurrentThread.CurrentCulture;
+            _defaultComparer = StringComparer.Create(_defaultCulture, true);
         }
 
         #endregion Constructors
@@ -224,17 +225,15 @@ internal IList GetSuggestionsForError(SpellingError error)
         // implement this as a process-wide list.
         internal void IgnoreAll(string word)
         {
-            if (_ignoredWordsList == null)
-            {
-                _ignoredWordsList = new ArrayList(1);
-            }
+            if (_ignoredWordsList is null)
+                _ignoredWordsList = new List<string>(1);
 
-            int index = _ignoredWordsList.BinarySearch(word, new CaseInsensitiveComparer(_defaultCulture));
+            int index = _ignoredWordsList.BinarySearch(word, _defaultComparer);
 
+            // If we didn't find the word, we're gonna add it to ignore list
             if (index < 0)
             {
                 // This is a new word to ignore.
-
                 // Add it the list so we don't flag it later.
                 _ignoredWordsList.Insert(~index, word);
 
@@ -944,7 +943,6 @@ private bool ScanTextSegment(SpellerInteropBase.ISpellerSegment textSegment, obj
         {
             TextMapCallbackData data = (TextMapCallbackData)o;
             SpellerInteropBase.ITextRange sTextRange = textSegment.TextRange;
-            char[] word;
 
             // Check if this segment falls outside the content range.
             // The region before/after the content is only for context --
@@ -963,8 +961,7 @@ private bool ScanTextSegment(SpellerInteropBase.ISpellerSegment textSegment, obj
             if (sTextRange.Length > 1) // Ignore single letter errors.
             {
                 // Check if the segment has been marked "ignore" by the user.
-                word = new char[sTextRange.Length];
-                Array.Copy(data.TextMap.Text, sTextRange.Start, word, 0, sTextRange.Length);
+                string word = new(data.TextMap.Text, sTextRange.Start, sTextRange.Length);
 
                 if (!IsIgnoredWord(word))
                 {
@@ -1438,17 +1435,7 @@ private bool ExpandToWordBreakCallback(SpellerInteropBase.ISpellerSegment textSe
         }
 
         // Returns true if a user has tagged the specified word with "Ignore All".
-        private bool IsIgnoredWord(char[] word)
-        {
-            bool isIgnoredWord = false;
-
-            if (_ignoredWordsList != null)
-            {
-                isIgnoredWord = _ignoredWordsList.BinarySearch(new string(word), new CaseInsensitiveComparer(_defaultCulture)) >= 0;
-            }
-
-            return isIgnoredWord;
-        }
+        private bool IsIgnoredWord(string word) => _ignoredWordsList?.BinarySearch(word, _defaultComparer) >= 0;
 
         // Returns true if we have an engine capable of proofing the specified
         // language.
@@ -2052,11 +2039,12 @@ internal object Lexicon
         private bool _pendingCaretMovedCallback;
 
         // List of words tagged by the user as non-errors.
-        private ArrayList _ignoredWordsList;
+        private List<string> _ignoredWordsList;
 
         // The CultureInfo associated with this speller.
         // Used for ignored words comparison, and plain text controls (TextBox).
         private readonly CultureInfo _defaultCulture;
+        private readonly IComparer<string> _defaultComparer;
 
         // Set true if the nl6 library is unavailable.
         private bool _failedToInit;