diff --git a/MMOCore-API/src/main/java/net/Indyuce/mmocore/command/rpg/admin/SlotCommandTreeNode.java b/MMOCore-API/src/main/java/net/Indyuce/mmocore/command/rpg/admin/SlotCommandTreeNode.java
index f7fd32fe..d274b5ca 100644
--- a/MMOCore-API/src/main/java/net/Indyuce/mmocore/command/rpg/admin/SlotCommandTreeNode.java
+++ b/MMOCore-API/src/main/java/net/Indyuce/mmocore/command/rpg/admin/SlotCommandTreeNode.java
@@ -53,7 +53,15 @@ public class SlotCommandTreeNode extends CommandTreeNode {
                 sender.sendMessage(ChatColor.RED + "The slot can't be negative.");
                 return CommandResult.FAILURE;
             }
+            if (slot > MMOCore.plugin.configManager.maxSkillSlots) {
+                sender.sendMessage(ChatColor.RED + "The slot can't be higher than " + MMOCore.plugin.configManager.maxSkillSlots + ".");
+                return CommandResult.FAILURE;
+            }
             SkillSlot skillSlot = playerData.getProfess().getSkillSlot(slot);
+            if(skillSlot.isUnlockedByDefault()){
+                sender.sendMessage(ChatColor.RED + "You can't lock a skill that is unlocked by default.");
+                return CommandResult.FAILURE;
+            }
             if (lock) {
                 if (!playerData.hasUnlocked(skillSlot)) {
                     CommandVerbose.verbose(sender, CommandVerbose.CommandType.SKILL, ChatColor.RED + "The skill slot " + skillSlot.getName() + " is already locked" + " for " + player.getName());