diff --git a/skimage/measure/_regionprops.py b/skimage/measure/_regionprops.py
index ee58868c..be10d6ec 100644
--- a/skimage/measure/_regionprops.py
+++ b/skimage/measure/_regionprops.py
@@ -124,7 +124,7 @@ def regionprops(label_image, properties=['Area', 'Centroid'],
         * Orientation : float
             Angle between the X-axis and the major axis of the ellipse that has
             the same second-moments as the region. Ranging from `-pi/2` to
-            `-pi/2` in counter-clockwise direction.
+            `pi/2` in counter-clockwise direction.
         * Perimeter : float
             Perimeter of object which approximates the contour as a line through
             the centers of border pixels using a 4-connectivity.
@@ -299,7 +299,10 @@ def regionprops(label_image, properties=['Area', 'Centroid'],
 
         if 'Orientation' in properties:
             if a - c == 0:
-                obj_props['Orientation'] = PI / 2
+                if b > 0:
+                    obj_props['Orientation'] = -PI / 4.
+                else:
+                    obj_props['Orientation'] = PI / 4.
             else:
                 obj_props['Orientation'] = - 0.5 * atan2(2 * b, (a - c))
 
diff --git a/skimage/measure/tests/test_regionprops.py b/skimage/measure/tests/test_regionprops.py
index 915087dc..7faf0bac 100644
--- a/skimage/measure/tests/test_regionprops.py
+++ b/skimage/measure/tests/test_regionprops.py
@@ -197,6 +197,15 @@ def test_orientation():
     # test correct quadrant determination
     orientation2 = regionprops(SAMPLE.T, ['Orientation'])[0]['Orientation']
     assert_almost_equal(orientation2, math.pi / 2 - orientation)
+    # test diagonal regions
+    orientation_diag = regionprops(np.eye(10, dtype=int), ['Orientation'])[0]['Orientation']
+    assert_almost_equal(orientation_diag, -math.pi / 4)
+    orientation_diag = regionprops(np.flipud(np.eye(10, dtype=int)), ['Orientation'])[0]['Orientation']
+    assert_almost_equal(orientation_diag, math.pi / 4)
+    orientation_diag = regionprops(np.fliplr(np.eye(10, dtype=int)), ['Orientation'])[0]['Orientation']
+    assert_almost_equal(orientation_diag, math.pi / 4)
+    orientation_diag = regionprops(np.fliplr(np.flipud(np.eye(10, dtype=int))), ['Orientation'])[0]['Orientation']
+    assert_almost_equal(orientation_diag, -math.pi / 4)
 
 def test_perimeter():
     perimeter = regionprops(SAMPLE, ['Perimeter'])[0]['Perimeter']