diff --git a/INSTALL b/INSTALL
index 679f0c7ba191..ebcb79493866 100644
--- a/INSTALL
+++ b/INSTALL
@@ -199,7 +199,10 @@ libpng 1.2 (or later)
 :term:`dateutil` 1.1 or later
     Provides extensions to python datetime handling.  If using pip,
     easy_install or installing from source, the installer will attempt
-    to download and install `python_dateutil` from PyPI.
+    to download and install `python_dateutil` from PyPI.  Note that
+    `python_dateutil` also depends on `six`.  `pip` and other package
+    managers should handle installing that secondary dependency
+    automatically.
 
 `pyparsing`
     Required for matplotlib's mathtext math rendering support.  If
diff --git a/doc/users/whats_new.rst b/doc/users/whats_new.rst
index 2017452f6cbf..962588bdb1fc 100644
--- a/doc/users/whats_new.rst
+++ b/doc/users/whats_new.rst
@@ -279,11 +279,12 @@ New setup script
 ````````````````
 matplotlib 1.3 includes an entirely rewritten setup script.  We now
 ship fewer dependencies with the tarballs and installers themselves.
-Notably, `pytz`, `dateutil` and `pyparsing` are no longer included
-with matplotlib.  You can either install them manually first, or let
-`pip` install them as dependencies along with matplotlib.  It is now
-possible to not include certain subcomponents, such as the unit test
-data, in the install.  See `setup.cfg.template` for more information.
+Notably, `pytz`, `dateutil`, `pyparsing` and `six` are no longer
+included with matplotlib.  You can either install them manually first,
+or let `pip` install them as dependencies along with matplotlib.  It
+is now possible to not include certain subcomponents, such as the unit
+test data, in the install.  See `setup.cfg.template` for more
+information.
 
 XDG base directory support
 ``````````````````````````