diff --git a/PIL/GifImagePlugin.py b/PIL/GifImagePlugin.py
index 7c9322754..9202a6d1b 100644
--- a/PIL/GifImagePlugin.py
+++ b/PIL/GifImagePlugin.py
@@ -386,6 +386,7 @@ def getheader(im, palette=None, info=None):
     # calculate the palette size for the header
     import math
     colorTableSize = math.ceil(math.log(len(paletteBytes)//3, 2))-1
+    if colorTableSize < 0: colorTableSize = 0
     s.append(o8(colorTableSize + 128)) # size of global color table + global color table flag
     s.append(o8(0) + o8(0)) # background + reserved/aspect
     # end of screen descriptor header
diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index 336aaba63..3d3d43a7e 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -25,4 +25,4 @@ def test_optimize():
         im.save(file, "GIF", optimize=optimize)
         return len(file.getvalue())
     assert_equal(test(0), 800)
-    assert_equal(test(1), 32)
+    assert_equal(test(1), 38)