diff --git a/doc/source/conf.py b/doc/source/conf.py
index e0ae6f6e..ebf4b1b7 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -28,7 +28,7 @@ sys.path.append(os.path.join(curpath, '..', 'ext'))
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['sphinx.ext.autodoc',
-              'sphinx.ext.pngmath',
+              'sphinx.ext.imgmath',
               'numpydoc',
               'sphinx.ext.autosummary',
               'plot2rst',
diff --git a/skimage/measure/_regionprops.py b/skimage/measure/_regionprops.py
index 297a6390..db376c27 100644
--- a/skimage/measure/_regionprops.py
+++ b/skimage/measure/_regionprops.py
@@ -112,6 +112,12 @@ class _RegionProperties(object):
         return np.sum(self.image)
 
     def bbox(self):
+        """
+        Returns
+        -------
+        A tuple of the bounding box's start coordinates for each dimension, 
+        followed by the end coordinates for each dimension
+        """
         return tuple([self._slice[i].start for i in range(self._ndim)] +
                      [self._slice[i].stop for i in range(self._ndim)])