diff --git a/docs/html/user_guide.rst b/docs/html/user_guide.rst
index 7706be28b..77974b00c 100644
--- a/docs/html/user_guide.rst
+++ b/docs/html/user_guide.rst
@@ -443,6 +443,11 @@ is the same as calling::
 
     pip install --find-links=http://mirror1.example.com --find-links=http://mirror2.example.com
 
+.. note::
+
+   Environment variables set to be empty string will not be treated as false. Please use ``no``,
+   ``false`` or ``0`` instead.
+
 
 Config Precedence
 -----------------
diff --git a/news/506D2F71-CA51-40F5-9D4B-F5502026CFCF.trivial b/news/506D2F71-CA51-40F5-9D4B-F5502026CFCF.trivial
new file mode 100644
index 000000000..e69de29bb