diff --git a/Plugins/Mineplex.Core/src/mineplex/core/account/CoreClientManager.java b/Plugins/Mineplex.Core/src/mineplex/core/account/CoreClientManager.java
index 9db17bce6..0bc28800c 100644
--- a/Plugins/Mineplex.Core/src/mineplex/core/account/CoreClientManager.java
+++ b/Plugins/Mineplex.Core/src/mineplex/core/account/CoreClientManager.java
@@ -17,7 +17,7 @@ import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
-import java.util.stream.Collectors;
+import java.util.regex.Pattern;
 
 import org.bukkit.Bukkit;
 import org.bukkit.entity.Player;
@@ -83,6 +83,8 @@ public class CoreClientManager extends MiniPlugin
 	}
 
 	private static final Map<String, Object> CLIENT_LOGIN_LOCKS = new ConcurrentHashMap<>();
+	
+	private static final Pattern VALID_USERNAME = Pattern.compile("[a-zA-Z0-9_]{1,16}");
 
 	private JavaPlugin _plugin;
 	private AccountRepository _repository;
@@ -365,6 +367,11 @@ public class CoreClientManager extends MiniPlugin
 
 	public void loadClientByName(String playerName, Consumer<CoreClient> loadedClient)
 	{
+		if (!VALID_USERNAME.matcher(playerName).find())
+		{
+			return;
+		}
+		
 		runAsync(() ->
 		{
 			AtomicReference<CoreClient> loaded = new AtomicReference<>();
@@ -436,6 +443,11 @@ public class CoreClientManager extends MiniPlugin
 
 	public void loadClientByNameSync(final String playerName, final Runnable runnable)
 	{
+		if (!VALID_USERNAME.matcher(playerName).find())
+		{
+			return;
+		}
+		
 		try
 		{
 			ClientToken token = null;