diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/versions/ModListPageSkin.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/versions/ModListPageSkin.java
index d0170a090..0af66f0e3 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/versions/ModListPageSkin.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/versions/ModListPageSkin.java
@@ -409,7 +409,8 @@ final class ModListPageSkin extends SkinBase<ModListPage> {
 
         @Override
         public int compareTo(@NotNull ModListPageSkin.ModInfoObject o) {
-            return localModFile.getFileName().toLowerCase().compareTo(o.localModFile.getFileName().toLowerCase());
+            return localModFile.getFileName().toLowerCase(Locale.ROOT)
+                    .compareTo(o.localModFile.getFileName().toLowerCase(Locale.ROOT));
         }
     }
 
diff --git a/HMCLCore/src/main/java/org/jackhuang/hmcl/mod/curse/CurseForgeRemoteModRepository.java b/HMCLCore/src/main/java/org/jackhuang/hmcl/mod/curse/CurseForgeRemoteModRepository.java
index 9ad325848..f884334c8 100644
--- a/HMCLCore/src/main/java/org/jackhuang/hmcl/mod/curse/CurseForgeRemoteModRepository.java
+++ b/HMCLCore/src/main/java/org/jackhuang/hmcl/mod/curse/CurseForgeRemoteModRepository.java
@@ -139,7 +139,7 @@ public final class CurseForgeRemoteModRepository implements RemoteModRepository
         StringUtils.LevCalculator levCalculator = new StringUtils.LevCalculator();
 
         return new SearchResult(response.getData().stream().map(CurseAddon::toMod).map(remoteMod -> {
-            String lowerCaseResult = remoteMod.getTitle().toLowerCase();
+            String lowerCaseResult = remoteMod.getTitle().toLowerCase(Locale.ROOT);
             int diff = levCalculator.calc(lowerCaseSearchFilter, lowerCaseResult);
 
             for (String s : StringUtils.tokenize(lowerCaseResult)) {
diff --git a/config/checkstyle/checkstyle.xml b/config/checkstyle/checkstyle.xml
index 223dc22f0..335e3ac2d 100644
--- a/config/checkstyle/checkstyle.xml
+++ b/config/checkstyle/checkstyle.xml
@@ -104,5 +104,17 @@
         <module name="RedundantImport"/> <!-- e.g. double import statements: http://checkstyle.sourceforge.net/config_imports.html#RedundantImport -->
         <module name="UnusedImports"/> <!-- http://checkstyle.sourceforge.net/config_imports.html#UnusedImports -->
         <module name="IllegalImport"/> <!-- checks if import sun.* is used http://checkstyle.sourceforge.net/config_imports.html#IllegalImport -->
+
+        <!--  Custom -->
+        <module name="RegexpSinglelineJava">
+            <property name="format" value="\.toLowerCase\(\)"/>
+            <property name="ignoreComments" value="true"/>
+            <property name="message" value="Should not use String#toLowerCase(), use String#toLowerCase(Locale.ROOT) instead."/>
+        </module>
+        <module name="RegexpSinglelineJava">
+            <property name="format" value="\.toUpperCase\(\)"/>
+            <property name="ignoreComments" value="true"/>
+            <property name="message" value="Should not use String#toUpperCase(), use String#toUpperCase(Locale.ROOT) instead."/>
+        </module>
     </module>
 </module>
\ No newline at end of file