diff --git a/PIL/ImagePalette.py b/PIL/ImagePalette.py
index ee3c22544..67bf593e6 100644
--- a/PIL/ImagePalette.py
+++ b/PIL/ImagePalette.py
@@ -134,7 +134,7 @@ def _make_linear_lut(black, white):
     return lut
 
 
-def _make_gamma_lut(exp, mode="RGB"):
+def make_gamma_lut(exp):
     lut = []
     for i in range(256):
         lut.append(int(((i / 255.0) ** exp) * 255.0 + 0.5))
diff --git a/Tests/test_imagepalette.py b/Tests/test_imagepalette.py
index be82f4dcb..af742edd1 100644
--- a/Tests/test_imagepalette.py
+++ b/Tests/test_imagepalette.py
@@ -44,6 +44,25 @@ class TestImagePalette(PillowTestCase):
         self.assertIsInstance(p, ImagePalette)
         self.assertEqual(p.palette, palette.tobytes())
 
+    def test_make_gamma_lut(self):
+        # Arrange
+        from PIL.ImagePalette import make_gamma_lut
+        exp = 5
+
+        # Act
+        lut = make_gamma_lut(exp)
+
+        # Assert
+        self.assertIsInstance(lut, list)
+        self.assertEqual(len(lut), 256)
+        # Check a few values
+        self.assertEqual(lut[0], 0)
+        self.assertEqual(lut[63], 0)
+        self.assertEqual(lut[127], 8)
+        self.assertEqual(lut[191], 60)
+        self.assertEqual(lut[255], 255)
+
+
 if __name__ == '__main__':
     unittest.main()