diff --git a/PIL/ImageMorph.py b/PIL/ImageMorph.py
index dcce63fa4..d2367737f 100644
--- a/PIL/ImageMorph.py
+++ b/PIL/ImageMorph.py
@@ -123,7 +123,7 @@ class LutBuilder(object):
                            .replace('0', 'Z')
                            .replace('1', '0')
                            .replace('Z', '1'))
-                res = '%d' % (1-int(res))
+                res = 1-int(res)
                 patterns.append((pattern, res))
 
         return patterns
@@ -152,8 +152,8 @@ class LutBuilder(object):
             patterns += self._pattern_permute(pattern, options, result)
 
 #        # Debugging
-#        for p,r in patterns:
-#            print(p,r)
+#        for p, r in patterns:
+#            print(p, r)
 #        print('--')
 
         # compile the patterns into regular expressions for speed
diff --git a/Tests/test_imagemorph.py b/Tests/test_imagemorph.py
index c0f6448e6..dac1ae150 100644
--- a/Tests/test_imagemorph.py
+++ b/Tests/test_imagemorph.py
@@ -184,7 +184,6 @@ class MorphTests(PillowTestCase):
         self.assertEqual(count, 7)
         self.assert_img_equal_img_string(Aout,
                                          """
-
                                          .......
                                          .......
                                          ..1.1..
@@ -194,6 +193,23 @@ class MorphTests(PillowTestCase):
                                          .......
                                          """)
 
+    def test_negate(self):
+        # Test 'N' for negate
+        mop = ImageMorph.MorphOp(patterns=['1:(... ... ...)->0',
+                                           'N:(00. 01. ...)->1'])
+        count, Aout = mop.apply(self.A)
+        self.assertEqual(count, 8)
+        self.assert_img_equal_img_string(Aout,
+                                         """
+                                         .......
+                                         .......
+                                         ..1....
+                                         .......
+                                         .......
+                                         .......
+                                         .......
+                                         """)
+
     def test_non_binary_images(self):
         im = hopper('RGB')
         mop = ImageMorph.MorphOp(op_name="erosion8")