diff --git a/en/reference/association-mapping.rst b/en/reference/association-mapping.rst
index bd46217a1..1b42dcc3f 100644
--- a/en/reference/association-mapping.rst
+++ b/en/reference/association-mapping.rst
@@ -384,6 +384,11 @@ Or you can trigger the validation manually:
 If the mapping is invalid the errors array contains a positive
 number of elements with error messages.
 
+.. warning::
+
+    One mapping option that is not validated is the use of the referenced column name.
+    It has to point to the equivalent primary key otherwise Doctrine will not work.
+
 .. note::
 
     One common error is to use a backlash in front of the