diff --git a/lib/src/darwin/native.dart b/lib/src/darwin/native.dart
index a68e864..2511820 100644
--- a/lib/src/darwin/native.dart
+++ b/lib/src/darwin/native.dart
@@ -345,9 +345,11 @@ final class ImageConverterDarwin implements ImageConverterPlatform {
       final keys = arena<Pointer<Void>>(3);
       final values = arena<Pointer<Void>>(3);
 
-      // kCGImageSourceCreateThumbnailFromImageIfAbsent = kCFBooleanTrue
-      // Use 1.toNSNumber() — bool has no toNSNumber() extension; NSNumber(1) = YES.
-      keys[0] = kCGImageSourceCreateThumbnailFromImageIfAbsent.cast();
+      // kCGImageSourceCreateThumbnailFromImageAlways = kCFBooleanTrue
+      // MUST use "Always" not "IfAbsent": iPhone HEIC files embed a tiny
+      // ~240x320 JPEG thumbnail. "IfAbsent" returns that embedded thumbnail
+      // instead of decoding the full image, giving very low-resolution output.
+      keys[0] = kCGImageSourceCreateThumbnailFromImageAlways.cast();
       values[0] = 1.toNSNumber().ref.retainAndAutorelease().cast();
 
       // kCGImageSourceCreateThumbnailWithTransform = kCFBooleanTrue
diff --git a/lib/src/darwin/orientation_bindings.dart b/lib/src/darwin/orientation_bindings.dart
index 660f669..5528582 100644
--- a/lib/src/darwin/orientation_bindings.dart
+++ b/lib/src/darwin/orientation_bindings.dart
@@ -85,6 +85,17 @@ external ffi.Pointer<objc.CFString> kCGImagePropertyOrientation;
 @ffi.Native<ffi.Pointer<objc.CFString>>()
 external ffi.Pointer<objc.CFString> kCGImageSourceCreateThumbnailFromImageIfAbsent;
 
+/// Key: when `kCFBooleanTrue`, ALWAYS creates a thumbnail from the full source
+/// image data, ignoring any embedded thumbnail.
+///
+/// **Use this instead of [kCGImageSourceCreateThumbnailFromImageIfAbsent] when
+/// full-resolution output is required.** iPhone HEIC files always contain a
+/// tiny embedded JPEG thumbnail (~240×320). Without this key, ImageIO returns
+/// the embedded thumbnail rather than decoding the full image, producing a very
+/// low-resolution output regardless of [kCGImageSourceThumbnailMaxPixelSize].
+@ffi.Native<ffi.Pointer<objc.CFString>>()
+external ffi.Pointer<objc.CFString> kCGImageSourceCreateThumbnailFromImageAlways;
+
 /// Key: when `kCFBooleanTrue`, rotates/flips the thumbnail to match the EXIF
 /// orientation tag, producing pixel-correct upright image data.
 @ffi.Native<ffi.Pointer<objc.CFString>>()