diff --git a/PIL/PngImagePlugin.py b/PIL/PngImagePlugin.py
index 53d38eecd..214ff9385 100644
--- a/PIL/PngImagePlugin.py
+++ b/PIL/PngImagePlugin.py
@@ -71,6 +71,7 @@ _MODES = {
 
 
 _simple_palette = re.compile(b'^\xff+\x00\xff*$')
+_null_palette = re.compile(b'^\x00*$')
 
 # Maximum decompressed size for a iTXt or zTXt chunk.
 # Eliminates decompression bombs where compressed chunks can expand 1000x
@@ -350,6 +351,8 @@ class PngStream(ChunkStream):
                 i = s.find(b"\0")
                 if i >= 0:
                     self.im_info["transparency"] = i
+            elif _null_palette.match(s):
+                self.im_info["transparency"] = 0
             else:
                 self.im_info["transparency"] = s
         elif self.im_mode == "L":
diff --git a/Tests/images/tRNS_null_1x1.png b/Tests/images/tRNS_null_1x1.png
new file mode 100644
index 000000000..976eae939
Binary files /dev/null and b/Tests/images/tRNS_null_1x1.png differ
diff --git a/Tests/test_file_png.py b/Tests/test_file_png.py
index b3169ed25..f438e24cc 100644
--- a/Tests/test_file_png.py
+++ b/Tests/test_file_png.py
@@ -354,6 +354,13 @@ class TestFilePng(PillowTestCase):
         self.assert_image_equal(im2.convert('RGBA'),
                                 im.convert('RGBA'))
 
+    def test_trns_null(self):
+        # Check reading images with null tRNS value, issue #1239
+        test_file = "Tests/images/tRNS_null_1x1.png"
+        im = Image.open(test_file)
+
+        self.assertEqual(im.info["transparency"], 0)
+
     def test_save_icc_profile_none(self):
         # check saving files with an ICC profile set to None (omit profile)
         in_file = "Tests/images/icc_profile_none.png"