diff --git a/spec/API_specification/dataframe_api/dataframe_object.py b/spec/API_specification/dataframe_api/dataframe_object.py
index 0fd0eed8..bf9643e6 100644
--- a/spec/API_specification/dataframe_api/dataframe_object.py
+++ b/spec/API_specification/dataframe_api/dataframe_object.py
@@ -932,6 +932,10 @@ def join(
         """
         Join with other dataframe.
 
+        Other than the joining column name(s), no column name is allowed to appear in
+        both `self` and `other`. Rename columns before calling `join` if necessary
+        using :meth:`rename_columns`.
+
         Parameters
         ----------
         other : DataFrame
@@ -951,4 +955,10 @@ def join(
         Returns
         -------
         DataFrame
+
+        Raises
+        ------
+        ValueError
+            If, apart from `left_on` and `right_on`, there are any column names
+            present in both `self` and `other`.
         """