diff --git a/src/main/java/emu/grasscutter/Grasscutter.java b/src/main/java/emu/grasscutter/Grasscutter.java
index 823633c4f..89c4d8a26 100644
--- a/src/main/java/emu/grasscutter/Grasscutter.java
+++ b/src/main/java/emu/grasscutter/Grasscutter.java
@@ -149,7 +149,13 @@ public final class Grasscutter {
 
 	public static void loadLanguage() {
 		var locale = config.LocaleLanguage;
-		language = Language.getLanguage(locale.toLanguageTag());
+		String languageTag = locale.toLanguageTag();
+		if (languageTag.equals("und")) {
+			Grasscutter.getLogger().error("Illegal locale language, using en-US instead.");
+			language = Language.getLanguage("en-US");
+		} else {
+			language = Language.getLanguage(languageTag);
+		}
 	}
 
 	public static void saveConfig() {