diff --git a/Tests/test_file_png.py b/Tests/test_file_png.py
index be52b3bd1..408a76444 100644
--- a/Tests/test_file_png.py
+++ b/Tests/test_file_png.py
@@ -86,6 +86,7 @@ class TestFilePng(PillowTestCase):
         self.assertEqual(im.mode, "RGB")
         self.assertEqual(im.size, (128, 128))
         self.assertEqual(im.format, "PNG")
+        self.assertEqual(im.get_format_mimetype(), 'image/png')
 
         hopper("1").save(test_file)
         Image.open(test_file)
@@ -589,6 +590,8 @@ class TestFilePng(PillowTestCase):
                          "WebP support not installed with animation")
     def test_apng(self):
         im = Image.open("Tests/images/iss634.apng")
+        self.assertEqual(im.get_format_mimetype(), 'image/apng')
+
         expected = Image.open("Tests/images/iss634.webp")
         self.assert_image_similar(im, expected, 0.23)
 
diff --git a/src/PIL/ImageFile.py b/src/PIL/ImageFile.py
index 915557a57..bcc910853 100644
--- a/src/PIL/ImageFile.py
+++ b/src/PIL/ImageFile.py
@@ -79,6 +79,8 @@ class ImageFile(Image.Image):
 
         self._min_frame = 0
 
+        self.custom_mimetype = None
+
         self.tile = None
         self.readonly = 1  # until we know better
 
@@ -120,7 +122,7 @@ class ImageFile(Image.Image):
     def get_format_mimetype(self):
         if self.format is None:
             return
-        return Image.MIME.get(self.format.upper())
+        return self.custom_mimetype or Image.MIME.get(self.format.upper())
 
     def verify(self):
         "Check file integrity"
diff --git a/src/PIL/PngImagePlugin.py b/src/PIL/PngImagePlugin.py
index 04161a56c..d8ef56d73 100644
--- a/src/PIL/PngImagePlugin.py
+++ b/src/PIL/PngImagePlugin.py
@@ -296,6 +296,7 @@ class PngStream(ChunkStream):
         self.im_mode = None
         self.im_tile = None
         self.im_palette = None
+        self.im_custom_mimetype = None
 
         self.text_memory = 0
 
@@ -529,6 +530,7 @@ class PngStream(ChunkStream):
     # APNG chunks
     def chunk_acTL(self, pos, length):
         s = ImageFile._safe_read(self.fp, length)
+        self.im_custom_mimetype = 'image/apng'
         return s
 
     def chunk_fcTL(self, pos, length):
@@ -594,6 +596,7 @@ class PngImageFile(ImageFile.ImageFile):
         self.info = self.png.im_info
         self._text = None
         self.tile = self.png.im_tile
+        self.custom_mimetype = self.png.im_custom_mimetype
 
         if self.png.im_palette:
             rawmode, data = self.png.im_palette
@@ -908,4 +911,3 @@ Image.register_save(PngImageFile.format, _save)
 Image.register_extensions(PngImageFile.format, [".png", ".apng"])
 
 Image.register_mime(PngImageFile.format, "image/png")
-Image.register_mime(PngImageFile.format, "image/apng")