diff --git a/paper/src/main/java/ru/bk/oharass/freedomchat/FreedomChat.java b/paper/src/main/java/ru/bk/oharass/freedomchat/FreedomChat.java
index b8dfba3..ad1529e 100644
--- a/paper/src/main/java/ru/bk/oharass/freedomchat/FreedomChat.java
+++ b/paper/src/main/java/ru/bk/oharass/freedomchat/FreedomChat.java
@@ -1,5 +1,6 @@
 package ru.bk.oharass.freedomchat;
 
+import io.papermc.paper.util.MappingEnvironment;
 import net.kyori.adventure.key.Key;
 import org.bukkit.configuration.file.FileConfiguration;
 import org.bukkit.event.Listener;
@@ -20,6 +21,12 @@ public void onEnable() {
             this.getServer().getPluginManager().disablePlugin(this);
             return;
         }
+        if (!Boolean.getBoolean("im.evan.freedomchat.bypassmappingscheck") && MappingEnvironment.reobf()) {
+            getLogger().warning("This version of FreedomChat only supports Mojang-mapped servers. Please use the Mojang-mapped server JAR");
+            getLogger().warning("If you know what you are doing, set the im.evan.freedomchat.bypassmappingscheck system property to true to bypass this check");
+            this.getServer().getPluginManager().disablePlugin(this);
+            return;
+        }
 
         this.saveDefaultConfig();
         final FileConfiguration config = this.getConfig();