diff --git a/user_guide_src/source/database/forge.rst b/user_guide_src/source/database/forge.rst
index a875f74..646e3a5 100644
--- a/user_guide_src/source/database/forge.rst
+++ b/user_guide_src/source/database/forge.rst
@@ -143,6 +143,8 @@
 	$this->dbforge->add_field("label varchar(100) NOT NULL DEFAULT 'default label'");
 
 
+.. note:: Passing raw strings as fields cannot be followed by ``add_key()`` calls on those fields.
+
 .. note:: Multiple calls to add_field() are cumulative.
 
 Creating an id field