diff --git a/PluralKit.Bot/Proxy/ProxyService.cs b/PluralKit.Bot/Proxy/ProxyService.cs
index 4ab45e4f..abdd4180 100644
--- a/PluralKit.Bot/Proxy/ProxyService.cs
+++ b/PluralKit.Bot/Proxy/ProxyService.cs
@@ -118,6 +118,10 @@ public class ProxyService
         if (msg.Author.System == true || msg.Author.Bot || msg.WebhookId != null)
             throw new ProxyChecksFailedException("This message was not sent by a normal user.");
 
+        // Make sure this message does not start a forum thread
+        if (msg.Id == msg.ChannelId)
+            throw new ProxyChecksFailedException("This message is the initial message in a forum post, which PluralKit is unable to proxy correctly.");
+
         // Make sure proxying is enabled here
         if (ctx.InBlacklist)
             throw new ProxyChecksFailedException(
@@ -501,4 +505,4 @@ public class ProxyService
     {
         public ProxyChecksFailedException(string message) : base(message) { }
     }
-}
+}
\ No newline at end of file