diff --git a/NEWS.md b/NEWS.md
index e999833..1d6b466 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,9 @@
 # 📰 Picopt News
 
+## v6.3.1
+
+- Fix frame duration erroneously extracted for MPO format, causing an error.
+
 ## v6.3.0
 
 - New progress and logging
diff --git a/picopt/walk/detect_format.py b/picopt/walk/detect_format.py
index c652696..822989b 100644
--- a/picopt/walk/detect_format.py
+++ b/picopt/walk/detect_format.py
@@ -31,6 +31,7 @@
 from contextlib import suppress
 from typing import TYPE_CHECKING, Any, BinaryIO
 
+from loguru import logger
 from PIL import Image, ImageSequence, UnidentifiedImageError
 
 from picopt import plugins as registry
@@ -41,18 +42,40 @@
 if TYPE_CHECKING:
     from collections.abc import Mapping
 
-    import PIL.ImageFile
+    from PIL.ImageFile import ImageFile
 
     from picopt.path import PathInfo
 
 # PIL format-string constants. Hardcoded so this module doesn't have to
 # import the per-format PIL ImageFile subclasses just to read a string.
-_WEBP_FORMAT_STR = "WEBP"
+_MPO_FORMAT_STR = "MPO"
 _TIFF_FORMAT_STR = "TIFF"
+_WEBP_FORMAT_STR = "WEBP"
+
+
+def _extract_animated_durations(image: ImageFile, info: dict[str, Any]):
+    durations = {}
+    if image.format == _MPO_FORMAT_STR:
+        return durations
+
+    # PIL frequently fails to populate per-frame durations on WebP
+    if image.format != _WEBP_FORMAT_STR and info.get("durations"):
+        return durations
+
+    try:
+        for frame_index, frame in enumerate(ImageSequence.Iterator(image), start=1):
+            duration = frame.info.get("duration", None)
+            if duration is not None:
+                durations[frame_index] = duration
+    except Exception as exc:
+        msg = "Error extracting animated frame duration"
+        logger.warning(msg)
+        logger.exception(exc)
+    return durations
 
 
 def _extract_image_info_from_image(
-    image: PIL.ImageFile.ImageFile, info: dict[str, Any], *, keep_metadata: bool
+    image: ImageFile, info: dict[str, Any], *, keep_metadata: bool
 ) -> None:
     image_format_str = image.format
     if not image_format_str:
@@ -67,14 +90,7 @@ def _extract_image_info_from_image(
     info["animated"] = animated
     if animated and (n_frames := getattr(image, "n_frames", 0)):
         info["n_frames"] = n_frames
-        # PIL frequently fails to populate per-frame durations on WebP, so
-        # walk the sequence ourselves.
-        durations = {}
-        for frame_index, frame in enumerate(ImageSequence.Iterator(image), start=1):
-            duration = frame.info.get("duration", None)
-            if duration is not None:
-                durations[frame_index] = duration
-        if durations:
+        if durations := _extract_animated_durations(image, info):
             info["durations"] = durations
     with suppress(AttributeError):
         info["mpinfo"] = image.mpinfo  # pyright: ignore[reportAttributeAccessIssue]  # ty: ignore[unresolved-attribute]
diff --git a/pyproject.toml b/pyproject.toml
index 99bb77d..d86d0d0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,7 +35,7 @@ readme = "README.md"
 requires-python = ">=3.10"
 license = { text = "GPL-3.0-only" }
 name = "picopt"
-version = "6.3.0"
+version = "6.3.1"
 [[project.authors]]
 name = "AJ Slater"
 email = "aj@slater.net"
diff --git a/uv.lock b/uv.lock
index f6db4d2..8c793a7 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1598,7 +1598,7 @@ wheels = [
 
 [[package]]
 name = "picopt"
-version = "6.3.0"
+version = "6.3.1"
 source = { editable = "." }
 dependencies = [
     { name = "confuse" },