diff --git a/PIL/Image.py b/PIL/Image.py
index b4b4a0a11..95fda90d2 100644
--- a/PIL/Image.py
+++ b/PIL/Image.py
@@ -1374,16 +1374,17 @@ class Image(object):
             self.im.paste(im, box)
 
     def alpha_composite(self, im, dest=(0,0), source=(0,0)):
-        """ 'In-place' analog of Image.alpha_composite
+        """ 'In-place' analog of Image.alpha_composite. Composites an image
+        onto this image.
 
         :param im: image to composite over this one
-        :param dest: Optional 2 tuple specificing the upper left corner
-          in the this image.
-        :param source: Optional 2 or 4 tuple, (x0, y0) for the upper
-          left corner in the source image. If a 4 tuple, the bounds of
-          the source rectangle.
+        :param dest: Optional 2 tuple (top, left) specifying the upper
+          left corner in this (destination) image.
+        :param source: Optional 2 (top, left) tuple for the upper left
+          corner in the overlay source image, or 4 tuple (top, left, bottom,
+          right) for the bounds of the source rectangle
           
-        Note: Not currently implemented in-place.
+        Performance Note: Not currently implemented in-place in the core layer.
         """
 
         if not isinstance(source, tuple):
diff --git a/docs/reference/Image.rst b/docs/reference/Image.rst
index 6dcc816e5..3335cb3da 100644
--- a/docs/reference/Image.rst
+++ b/docs/reference/Image.rst
@@ -104,6 +104,8 @@ An instance of the :py:class:`~PIL.Image.Image` class has the following
 methods. Unless otherwise stated, all methods return a new instance of the
 :py:class:`~PIL.Image.Image` class, holding the resulting image.
 
+
+.. automethod:: PIL.Image.Image.alpha_composite
 .. automethod:: PIL.Image.Image.convert
 
 The following example converts an RGB image (linearly calibrated according to