diff --git a/Tests/images/test_extents.gif b/Tests/images/test_extents.gif
new file mode 100644
index 00000000000..03c436435d6
Binary files /dev/null and b/Tests/images/test_extents.gif differ
diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index 8388949888d..f9c31212469 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -663,3 +663,9 @@ def test_lzw_bits(self):
         self.assertEqual(im.tile[0][3][0], 11)  # LZW bits
         # codec error prepatch
         im.load()
+
+    def test_extents(self):
+        im = Image.open('Tests/images/test_extents.gif')
+        self.assertEqual(im.size, (100, 100))
+        im.seek(1)
+        self.assertEqual(im.size, (150, 150))
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index 3dc13ac0392..5605b558147 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -233,6 +233,8 @@ def _seek(self, frame):
                 # extent
                 x0, y0 = i16(s[0:]), i16(s[2:])
                 x1, y1 = x0 + i16(s[4:]), y0 + i16(s[6:])
+                if x1 > self.size[0] or y1 > self.size[1]:
+                    self._size = max(x1, self.size[0]), max(y1, self.size[1])
                 self.dispose_extent = x0, y0, x1, y1
                 flags = i8(s[8])