diff --git a/docs/ext/commands/api.rst b/docs/ext/commands/api.rst
index d983d1f1e..ddbd6325c 100644
--- a/docs/ext/commands/api.rst
+++ b/docs/ext/commands/api.rst
@@ -196,6 +196,9 @@ Errors
 .. autoexception:: discord.ext.commands.BadArgument
     :members:
 
+.. autoexception:: discord.ext.commands.BadUnionArgument
+    :members:
+
 .. autoexception:: discord.ext.commands.NoPrivateMessage
     :members: