diff --git a/TODO.txt b/TODO.txt
index db7ffe48..29d1ebac 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -6,6 +6,7 @@ Version 0.10
 * Remove {`ratio`, `sigma`} deprecation warnings of `skimage.segmentation.slic`
 * Change default mode of random_walker segmentation to 'cg_mg' > 'cg' > 'bf',
   depending on which optional dependencies are available.
+* Remove deprecated `out` parameter of `skimage.morphology.binary_*`
 
 Version 0.9
 -----------
diff --git a/skimage/morphology/binary.py b/skimage/morphology/binary.py
index d248d8db..11a14d49 100644
--- a/skimage/morphology/binary.py
+++ b/skimage/morphology/binary.py
@@ -1,3 +1,4 @@
+import warnings
 import numpy as np
 from scipy import ndimage
 
@@ -15,6 +16,9 @@ def _convolve(image, selem, out, cval):
     if out is None:
         out = np.zeros_like(image, dtype=out_dtype)
     else:
+        warnings.warn('Parameter `out` is deprecated and it does not equal '
+                      'the output image if the sum of the structuring element '
+                      'overflows the dtype of `out`.')
         iinfo = np.iinfo(out.dtype)
         if iinfo.max - iinfo.min < selem_sum:
             raise ValueError('Sum of structuring (=%d) element results in '