diff --git a/DEPENDS.txt b/DEPENDS.txt
index 2130e21d..2c2aeb7d 100644
--- a/DEPENDS.txt
+++ b/DEPENDS.txt
@@ -56,3 +56,10 @@ Testing requirements
       A Python Unit Testing Framework
 * `Coverage.py <http://nedbatchelder.com/code/coverage/>`__
       A tool that generates a unit test code coverage report
+
+
+Documentation requirements
+--------------------------
+
+`sphinx >= 1.3 <http://sphinx-doc.org/>`_ is required to build the
+documentation.
diff --git a/doc/README.md b/doc/README.md
index d9fec89a..d11b92dd 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -2,7 +2,7 @@
 To build docs, run `make` in this directory. `make help` lists all targets.
 
 ## Requirements ##
-Sphinx and Latex is needed to build doc.
+Sphinx (>= 1.3) and Latex is needed to build doc.
 
 **Sphinx:**
 ```sh
diff --git a/doc/source/user_guide/transforming_image_data.txt b/doc/source/user_guide/transforming_image_data.txt
index 9dfe3139..f5b92e45 100644
--- a/doc/source/user_guide/transforming_image_data.txt
+++ b/doc/source/user_guide/transforming_image_data.txt
@@ -122,7 +122,7 @@ the image. The histogram of pixel values is computed with
 
 :func:`histogram` returns the number of pixels for each value bin, and
 the centers of the bins. The behavior of :func:`histogram` is therefore
-slightly different from the one of :func:`np.histogram`, which returns
+slightly different from the one of :func:`numpy.histogram`, which returns
 the boundaries of the bins.
 
 The simplest contrast enhancement :func:`rescale_intensity` consists in