diff --git a/scikits/image/filter/edges.py b/scikits/image/filter/edges.py
index 8ffeee8e..b0ea9a54 100644
--- a/scikits/image/filter/edges.py
+++ b/scikits/image/filter/edges.py
@@ -67,9 +67,10 @@ def hsobel(image, mask=None):
     big_mask = binary_erosion(mask,
                               generate_binary_structure(2, 2),
                               border_value = 0)
-    result = np.abs(convolve(image, np.array([[ 1, 2, 1],
-                                              [ 0, 0, 0],
-                                              [-1,-2,-1]]).astype(float) / 4.0))
+    result = np.abs(convolve(image.astype(float),
+                             np.array([[ 1, 2, 1],
+                                       [ 0, 0, 0],
+                                       [-1,-2,-1]]).astype(float) / 4.0))
     result[big_mask == False] = 0
     return result
 
@@ -103,9 +104,10 @@ def vsobel(image, mask=None):
     big_mask = binary_erosion(mask,
                               generate_binary_structure(2, 2),
                               border_value=0)
-    result = np.abs(convolve(image, np.array([[1, 0, -1],
-                                              [2, 0, -2],
-                                              [1, 0, -1]]).astype(float) / 4.0))
+    result = np.abs(convolve(image.astype(float),
+                             np.array([[1, 0, -1],
+                                       [2, 0, -2],
+                                       [1, 0, -1]]).astype(float) / 4.0))
     result[big_mask == False] = 0
     return result
 
@@ -161,9 +163,10 @@ def hprewitt(image, mask=None):
     big_mask = binary_erosion(mask,
                               generate_binary_structure(2, 2),
                               border_value=0)
-    result = np.abs(convolve(image, np.array([[ 1, 1, 1],
-                                              [ 0, 0, 0],
-                                              [-1,-1,-1]]).astype(float) / 3.0))
+    result = np.abs(convolve(image.astype(float),
+                             np.array([[ 1, 1, 1],
+                                       [ 0, 0, 0],
+                                       [-1,-1,-1]]).astype(float) / 3.0))
     result[big_mask == False] = 0
     return result
 
@@ -197,8 +200,9 @@ def vprewitt(image, mask=None):
     big_mask = binary_erosion(mask,
                               generate_binary_structure(2, 2),
                               border_value=0)
-    result = np.abs(convolve(image, np.array([[1, 0, -1],
-                                              [1, 0, -1],
-                                              [1, 0, -1]]).astype(float) / 3.0))
+    result = np.abs(convolve(image.astype(float),
+                             np.array([[1, 0, -1],
+                                       [1, 0, -1],
+                                       [1, 0, -1]]).astype(float) / 3.0))
     result[big_mask == False] = 0
     return result
diff --git a/scikits/image/filter/tests/test_edges.py b/scikits/image/filter/tests/test_edges.py
index 7f296b7f..fb900d72 100644
--- a/scikits/image/filter/tests/test_edges.py
+++ b/scikits/image/filter/tests/test_edges.py
@@ -1,7 +1,11 @@
+import os
+
 from numpy.testing import *
 import numpy as np
 from scipy.ndimage import binary_dilation, binary_erosion
+
 import scikits.image.filter as F
+from scikits.image import data_dir
 
 class TestSobel():
     def test_00_00_zeros(self):
@@ -35,6 +39,16 @@ class TestSobel():
         assert (np.all(result[j == 0] == 1))
         assert (np.all(result[np.abs(j) > 1] == 0))
 
+    def test_convolution_upcast(self):
+        i, j = np.mgrid[-5:6, -5:6]
+        image = np.load(os.path.join(data_dir, 'lena_GRAY_U8.npy'))
+
+        result1 = F.sobel(image)
+        image = image.astype(float)
+        result2 = F.sobel(image)
+
+        assert_array_equal(result1, result2)
+
 class TestHSobel():
     def test_00_00_zeros(self):
         """Horizontal sobel on an array of all zeros"""