diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index 645bb26bf..12754ed57 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -535,8 +535,9 @@ def _write_local_header(fp, im, offset, flags):
                  o8(transparency) +       # transparency index
                  o8(0))
 
-    if "comment" in im.encoderinfo and \
-       1 <= len(im.encoderinfo["comment"]) <= 255:
+    if "comment" in im.encoderinfo \
+        and im.encoderinfo["comment"] is not None \
+        and 1 <= len(im.encoderinfo["comment"]) <= 255:
         fp.write(b"!" +
                  o8(254) +                # extension intro
                  o8(len(im.encoderinfo["comment"])) +
@@ -702,7 +703,8 @@ def _get_global_header(im, info):
     for extensionKey in ["transparency", "duration", "loop", "comment"]:
         if info and extensionKey in info:
             if ((extensionKey == "duration" and info[extensionKey] == 0) or
-                (extensionKey == "comment" and
+                (extensionKey == "comment"
+                 and info[extensionKey] is not None and
                  not (1 <= len(info[extensionKey]) <= 255))):
                 continue
             version = b"89a"