diff --git a/Tests/test_file_apng.py b/Tests/test_file_apng.py
index fffbc54caf5..d0c81b5e9d7 100644
--- a/Tests/test_file_apng.py
+++ b/Tests/test_file_apng.py
@@ -350,7 +350,7 @@ def test_apng_save(tmp_path):
         im.load()
         assert not im.is_animated
         assert im.n_frames == 1
-        assert im.get_format_mimetype() == "image/apng"
+        assert im.get_format_mimetype() == "image/png"
         assert im.info.get("default_image") is None
         assert im.getpixel((0, 0)) == (0, 255, 0, 255)
         assert im.getpixel((64, 32)) == (0, 255, 0, 255)
@@ -450,26 +450,29 @@ def test_apng_save_duration_loop(tmp_path):
         test_file, save_all=True, append_images=[frame, frame], duration=[500, 100, 150]
     )
     with Image.open(test_file) as im:
-        im.load()
         assert im.n_frames == 1
-        assert im.info.get("duration") == 750
+        assert "duration" not in im.info
 
-    # test info duration
-    frame.info["duration"] = 750
-    frame.save(test_file, save_all=True)
+    different_frame = Image.new("RGBA", (128, 64))
+    frame.save(
+        test_file,
+        save_all=True,
+        append_images=[frame, different_frame],
+        duration=[500, 100, 150],
+    )
     with Image.open(test_file) as im:
-        assert im.info.get("duration") == 750
-
+        assert im.n_frames == 2
+        assert im.info["duration"] == 600
 
-def test_apng_save_duplicate_duration(tmp_path):
-    test_file = str(tmp_path / "temp.png")
-    frame = Image.new("RGB", (1, 1))
+        im.seek(1)
+        assert im.info["duration"] == 150
 
-    # Test a single duration is correctly combined across duplicate frames
-    frame.save(test_file, save_all=True, append_images=[frame, frame], duration=500)
+    # test info duration
+    frame.info["duration"] = 300
+    frame.save(test_file, save_all=True, append_images=[frame, different_frame])
     with Image.open(test_file) as im:
-        assert im.n_frames == 1
-        assert im.info.get("duration") == 1500
+        assert im.n_frames == 2
+        assert im.info["duration"] == 600
 
 
 def test_apng_save_disposal(tmp_path):
@@ -674,7 +677,8 @@ def test_seek_after_close():
 
 @pytest.mark.parametrize("mode", ("RGBA", "RGB", "P"))
 @pytest.mark.parametrize("default_image", (True, False))
-def test_different_modes_in_later_frames(mode, default_image, tmp_path):
+@pytest.mark.parametrize("duplicate", (True, False))
+def test_different_modes_in_later_frames(mode, default_image, duplicate, tmp_path):
     test_file = str(tmp_path / "temp.png")
 
     im = Image.new("L", (1, 1))
@@ -682,7 +686,7 @@ def test_different_modes_in_later_frames(mode, default_image, tmp_path):
         test_file,
         save_all=True,
         default_image=default_image,
-        append_images=[Image.new(mode, (1, 1))],
+        append_images=[im.convert(mode) if duplicate else Image.new(mode, (1, 1), 1)],
     )
     with Image.open(test_file) as reloaded:
         assert reloaded.mode == mode
diff --git a/src/PIL/PngImagePlugin.py b/src/PIL/PngImagePlugin.py
index 1bd0f442f76..dbcdee1c2d7 100644
--- a/src/PIL/PngImagePlugin.py
+++ b/src/PIL/PngImagePlugin.py
@@ -1156,6 +1156,9 @@ def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
                 encoderinfo["duration"] = duration
             im_frames.append({"im": im_frame, "bbox": bbox, "encoderinfo": encoderinfo})
 
+    if len(im_frames) == 1 and not default_image:
+        return im_frames[0]["im"]
+
     # animation control
     chunk(
         fp,
@@ -1391,8 +1394,10 @@ def _save(im, fp, filename, chunk=putchunk, save_all=False):
         chunk(fp, b"eXIf", exif)
 
     if save_all:
-        _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
-    else:
+        im = _write_multiple_frames(
+            im, fp, chunk, rawmode, default_image, append_images
+        )
+    if im:
         ImageFile._save(im, _idat(fp, chunk), [("zip", (0, 0) + im.size, 0, rawmode)])
 
     if info: