diff --git a/PIL/GribStubImagePlugin.py b/PIL/GribStubImagePlugin.py
index 1fbfe61dc..33c8291ea 100644
--- a/PIL/GribStubImagePlugin.py
+++ b/PIL/GribStubImagePlugin.py
@@ -10,6 +10,7 @@
 #
 
 from . import Image, ImageFile
+from ._binary import i8
 
 _handler = None
 
@@ -28,7 +29,7 @@ def register_handler(handler):
 # Image adapter
 
 def _accept(prefix):
-    return prefix[0:4] == b"GRIB" and prefix[7] == b'\x01'
+    return prefix[0:4] == b"GRIB" and i8(prefix[7]) == 1
 
 
 class GribStubImageFile(ImageFile.StubImageFile):
diff --git a/Tests/images/WAlaska.wind.7days.grb b/Tests/images/WAlaska.wind.7days.grb
new file mode 100644
index 000000000..37f9fd9b5
Binary files /dev/null and b/Tests/images/WAlaska.wind.7days.grb differ
diff --git a/Tests/test_file_gribstub.py b/Tests/test_file_gribstub.py
index 79025d3b4..dc0fa22d7 100644
--- a/Tests/test_file_gribstub.py
+++ b/Tests/test_file_gribstub.py
@@ -1,21 +1,45 @@
 from helper import unittest, PillowTestCase, hopper
 
-from PIL import GribStubImagePlugin
+from PIL import GribStubImagePlugin, Image
+
+TEST_FILE = "Tests/images/WAlaska.wind.7days.grb"
 
 
 class TestFileGribStub(PillowTestCase):
 
+    def test_open(self):
+        # Act
+        im = Image.open(TEST_FILE)
+
+        # Assert
+        self.assertEqual(im.format, "GRIB")
+
+        # Dummy data from the stub
+        self.assertEqual(im.mode, "F")
+        self.assertEqual(im.size, (1, 1))
+
     def test_invalid_file(self):
+        # Arrange
         invalid_file = "Tests/images/flower.jpg"
 
+        # Act / Assert
         self.assertRaises(SyntaxError,
                           lambda:
                           GribStubImagePlugin.GribStubImageFile(invalid_file))
 
-    def test_save(self):
-        im = hopper()
+    def test_load(self):
+        # Arrange
+        im = Image.open(TEST_FILE)
 
+        # Act / Assert: stub cannot load without an implemented handler
+        self.assertRaises(IOError, im.load)
+
+    def test_save(self):
+        # Arrange
+        im = hopper()
         tmpfile = self.tempfile("temp.grib")
+
+        # Act / Assert: stub cannot save without an implemented handler
         self.assertRaises(IOError, lambda: im.save(tmpfile))