diff --git a/JL.Core/Dicts/DictUtils.cs b/JL.Core/Dicts/DictUtils.cs
index 16c01f1c..166f6bcc 100644
--- a/JL.Core/Dicts/DictUtils.cs
+++ b/JL.Core/Dicts/DictUtils.cs
@@ -1323,7 +1323,7 @@ internal static async Task InitializeKanjiCompositionDict()
                     int endIndex = lParts[2].IndexOf('[', StringComparison.Ordinal);
 
                     KanjiCompositionDict.Add(lParts[1].GetPooledString(),
-                        endIndex is -1 ? lParts[2] : lParts[2][..endIndex]);
+                        endIndex < 0 ? lParts[2] : lParts[2][..endIndex]);
                 }
 
                 else if (lParts.Length > 3)
@@ -1333,7 +1333,7 @@ internal static async Task InitializeKanjiCompositionDict()
                         if (lParts[j].Contains('J', StringComparison.Ordinal))
                         {
                             int endIndex = lParts[j].IndexOf('[', StringComparison.Ordinal);
-                            if (endIndex is not -1)
+                            if (endIndex >= 0)
                             {
                                 KanjiCompositionDict.Add(lParts[1].GetPooledString(), lParts[j][..endIndex]);
                                 break;
diff --git a/JL.Core/Lookup/LookupUtils.cs b/JL.Core/Lookup/LookupUtils.cs
index 510a2513..9f7f310e 100644
--- a/JL.Core/Lookup/LookupUtils.cs
+++ b/JL.Core/Lookup/LookupUtils.cs
@@ -379,7 +379,7 @@ private static List<LookupResult> SortLookupResults(IEnumerable<LookupResult> lo
                     ? Array.IndexOf(lookupResult.Readings, lookupResult.MatchedText)
                     : -1;
 
-                if (index is -1)
+                if (index < 0)
                 {
                     return 3;
                 }
@@ -429,7 +429,7 @@ private static List<LookupResult> SortLookupResults(IEnumerable<LookupResult> lo
                     ? Array.IndexOf(lookupResult.Readings, lookupResult.MatchedText)
                     : -1;
 
-                return index is not -1
+                return index >= 0
                     ? index
                     : int.MaxValue;
             })
@@ -473,7 +473,7 @@ private static (bool tryLongVowelConversion, int succAttempt) GetWordResultsHelp
                             if (r.MatchedText == deconjugationResult.OriginalText)
                             {
                                 int index = r.Results.FindIndex(rs => rs.SequenceEqual(resultsList));
-                                if (index is not -1)
+                                if (index >= 0)
                                 {
                                     //if (!r.Processes?[index].Any(p => p.SequenceEqual(deconjugationResult.Process)) ?? false)
                                     r.Processes?[index].Add(deconjugationResult.Process);
diff --git a/JL.Core/Utilities/JapaneseUtils.cs b/JL.Core/Utilities/JapaneseUtils.cs
index e4bc1487..a9cb5704 100644
--- a/JL.Core/Utilities/JapaneseUtils.cs
+++ b/JL.Core/Utilities/JapaneseUtils.cs
@@ -201,7 +201,7 @@ public static string KatakanaToHiragana(string text)
         normalizedText = normalizedText.ToUpperInvariant();
 
         int firstKatakanaIndex = FirstKatakanaIndex(normalizedText);
-        if (firstKatakanaIndex is -1)
+        if (firstKatakanaIndex < 0)
         {
             return normalizedText;
         }
@@ -339,7 +339,7 @@ internal static string FindSentence(string text, int position)
 
             tempIndex = text.IndexOf(terminatingCharacter, position);
 
-            if (tempIndex is not -1 && (endPosition is -1 || tempIndex < endPosition))
+            if (tempIndex >= 0 && (endPosition < 0 || tempIndex < endPosition))
             {
                 endPosition = tempIndex;
             }
@@ -347,7 +347,7 @@ internal static string FindSentence(string text, int position)
 
         ++startPosition;
 
-        if (endPosition is -1)
+        if (endPosition < 0)
         {
             endPosition = text.Length - 1;
         }
@@ -431,7 +431,7 @@ private static int FirstPunctuationIndex(ReadOnlySpan<char> text)
     public static string RemovePunctuation(string text)
     {
         int index = FirstPunctuationIndex(text);
-        if (index is -1)
+        if (index < 0)
         {
             return text;
         }
diff --git a/JL.Core/Utilities/TextUtils.cs b/JL.Core/Utilities/TextUtils.cs
index 0ee0c70a..1d92daea 100644
--- a/JL.Core/Utilities/TextUtils.cs
+++ b/JL.Core/Utilities/TextUtils.cs
@@ -71,7 +71,7 @@ private static string RemoveInvalidUnicodeSequences(string text, int index)
     public static string SanitizeText(string text)
     {
         int firstInvalidUnicodeCharIndex = FirstInvalidUnicodeSequenceIndex(text);
-        if (firstInvalidUnicodeCharIndex is not -1)
+        if (firstInvalidUnicodeCharIndex >= 0)
         {
             text = RemoveInvalidUnicodeSequences(text, firstInvalidUnicodeCharIndex);
         }
diff --git a/JL.Windows/ConfigManager.cs b/JL.Windows/ConfigManager.cs
index f7cca7e6..292e851c 100644
--- a/JL.Windows/ConfigManager.cs
+++ b/JL.Windows/ConfigManager.cs
@@ -814,7 +814,7 @@ public static void LoadPreferenceWindow(PreferencesWindow preferenceWindow)
         preferenceWindow.MainWindowFontComboBox.SelectedIndex = Array.FindIndex(s_japaneseFonts, static f =>
             f.Content.ToString() == MainWindow.Instance.MainTextBox.FontFamily.Source);
 
-        if (preferenceWindow.MainWindowFontComboBox.SelectedIndex is -1)
+        if (preferenceWindow.MainWindowFontComboBox.SelectedIndex < 0)
         {
             preferenceWindow.MainWindowFontComboBox.SelectedIndex = 0;
         }
@@ -823,7 +823,7 @@ public static void LoadPreferenceWindow(PreferencesWindow preferenceWindow)
         preferenceWindow.PopupFontComboBox.SelectedIndex =
             Array.FindIndex(s_popupJapaneseFonts, static f => f.Content.ToString() == PopupFont.Source);
 
-        if (preferenceWindow.PopupFontComboBox.SelectedIndex is -1)
+        if (preferenceWindow.PopupFontComboBox.SelectedIndex < 0)
         {
             preferenceWindow.PopupFontComboBox.SelectedIndex = 0;
         }
@@ -855,7 +855,7 @@ public static void LoadPreferenceWindow(PreferencesWindow preferenceWindow)
         preferenceWindow.PopupXOffsetNumericUpDown.Value = PopupXOffset;
         preferenceWindow.PopupYOffsetNumericUpDown.Value = PopupYOffset;
 
-        if (preferenceWindow.LookupModeComboBox.SelectedIndex is -1)
+        if (preferenceWindow.LookupModeComboBox.SelectedIndex < 0)
         {
             preferenceWindow.LookupModeComboBox.SelectedIndex = 0;
         }
diff --git a/JL.Windows/GUI/MainWindow.xaml.cs b/JL.Windows/GUI/MainWindow.xaml.cs
index e6b12a62..e4882766 100644
--- a/JL.Windows/GUI/MainWindow.xaml.cs
+++ b/JL.Windows/GUI/MainWindow.xaml.cs
@@ -958,7 +958,7 @@ public void ShowAddNameWindow()
     {
         string? text = MainTextBox.SelectionLength > 0
             ? MainTextBox.SelectedText
-            : MainTextBox.GetCharacterIndexFromPoint(Mouse.GetPosition(MainTextBox), false) is not -1
+            : MainTextBox.GetCharacterIndexFromPoint(Mouse.GetPosition(MainTextBox), false) >= 0
               || (FirstPopupWindow.LastSelectedText is not null
                   && MainTextBox.Text.StartsWith(FirstPopupWindow.LastSelectedText, StringComparison.Ordinal))
                 ? FirstPopupWindow.LastSelectedText
@@ -991,7 +991,7 @@ public void ShowAddWordWindow()
     {
         string? text = MainTextBox.SelectionLength > 0
             ? MainTextBox.SelectedText
-            : MainTextBox.GetCharacterIndexFromPoint(Mouse.GetPosition(MainTextBox), false) is not -1
+            : MainTextBox.GetCharacterIndexFromPoint(Mouse.GetPosition(MainTextBox), false) >= 0
               || (FirstPopupWindow.LastSelectedText is not null
                   && MainTextBox.Text.StartsWith(FirstPopupWindow.LastSelectedText, StringComparison.Ordinal))
                 ? FirstPopupWindow.LastSelectedText
@@ -1014,7 +1014,7 @@ public void SearchWithBrowser()
     {
         string? text = MainTextBox.SelectionLength > 0
             ? MainTextBox.SelectedText
-            : MainTextBox.GetCharacterIndexFromPoint(Mouse.GetPosition(MainTextBox), false) is not -1
+            : MainTextBox.GetCharacterIndexFromPoint(Mouse.GetPosition(MainTextBox), false) >= 0
               || (FirstPopupWindow.LastSelectedText is not null
                   && MainTextBox.Text.StartsWith(FirstPopupWindow.LastSelectedText, StringComparison.Ordinal))
                 ? FirstPopupWindow.LastSelectedText
diff --git a/JL.Windows/GUI/PopupWindow.xaml.cs b/JL.Windows/GUI/PopupWindow.xaml.cs
index 9d59c0f4..4220fcff 100644
--- a/JL.Windows/GUI/PopupWindow.xaml.cs
+++ b/JL.Windows/GUI/PopupWindow.xaml.cs
@@ -307,7 +307,7 @@ public Task LookupOnMouseMoveOrClick(TextBox textBox)
     {
         int charPosition = textBox.GetCharacterIndexFromPoint(Mouse.GetPosition(textBox), false);
 
-        if (charPosition is not -1)
+        if (charPosition >= 0)
         {
             if (charPosition > 0 && char.IsHighSurrogate(textBox.Text[charPosition - 1]))
             {
@@ -1281,7 +1281,7 @@ private void SelectNextLookupResult()
 
     private void SelectPreviousLookupResult()
     {
-        int nextItemIndex = PopupListView.SelectedIndex - 1 > -1
+        int nextItemIndex = PopupListView.SelectedIndex - 1 >= 0
             ? PopupListView.SelectedIndex - 1
             : PopupListView.Items.Count - 1;