diff --git a/skimage/morphology/convex_hull.py b/skimage/morphology/convex_hull.py
index b045d7f3..565b10ab 100644
--- a/skimage/morphology/convex_hull.py
+++ b/skimage/morphology/convex_hull.py
@@ -38,7 +38,6 @@ def convex_hull_image(image):
     coords = possible_hull(image.astype(np.uint8))
     # repeated coordinates can *sometimes* cause problems in 
     # scipy.spatial.Delaunay, so we remove them.
-    coords = unique_rows(coords)
     N = len(coords)
 
     # Add a vertex for the middle of each pixel edge
@@ -47,7 +46,7 @@ def convex_hull_image(image):
                                                  (-0.5, 0.5, 0, 0))):
         coords_corners[i * N:(i + 1) * N] = coords + [x_offset, y_offset]
 
-    coords = coords_corners
+    coords = unique_rows(coords_corners)
 
     try:
         from scipy.spatial import Delaunay