diff --git a/docs/changelog.md b/docs/changelog.md
index 811e0bace..3db12151c 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -13,6 +13,9 @@ Requires libvips v8.13.1
 * Ensure auto-rotation works with shrink-on-load and extract (regression in 0.31.0).
   [#3352](https://github.com/lovell/sharp/issues/3352)
 
+* Ensure AVIF output is always 8-bit.
+  [#3358](https://github.com/lovell/sharp/issues/3358)
+
 ### v0.31.0 - 5th September 2022
 
 * Drop support for Node.js 12, now requires Node.js >= 14.15.0.
diff --git a/src/pipeline.cc b/src/pipeline.cc
index 5209d46b8..aa453b433 100644
--- a/src/pipeline.cc
+++ b/src/pipeline.cc
@@ -902,12 +902,13 @@ class PipelineWorker : public Napi::AsyncWorker {
         } else if (baton->formatOut == "heif" ||
           (baton->formatOut == "input" && inputImageType == sharp::ImageType::HEIF)) {
           // Write HEIF to buffer
-          image = sharp::RemoveAnimationProperties(image);
+          image = sharp::RemoveAnimationProperties(image).cast(VIPS_FORMAT_UCHAR);
           VipsArea *area = reinterpret_cast<VipsArea*>(image.heifsave_buffer(VImage::option()
             ->set("strip", !baton->withMetadata)
             ->set("Q", baton->heifQuality)
             ->set("compression", baton->heifCompression)
             ->set("effort", baton->heifEffort)
+            ->set("bitdepth", 8)
             ->set("subsample_mode", baton->heifChromaSubsampling == "4:4:4"
               ? VIPS_FOREIGN_SUBSAMPLE_OFF : VIPS_FOREIGN_SUBSAMPLE_ON)
             ->set("lossless", baton->heifLossless)));
@@ -1073,12 +1074,13 @@ class PipelineWorker : public Napi::AsyncWorker {
         } else if (baton->formatOut == "heif" || (mightMatchInput && isHeif) ||
           (willMatchInput && inputImageType == sharp::ImageType::HEIF)) {
           // Write HEIF to file
-          image = sharp::RemoveAnimationProperties(image);
+          image = sharp::RemoveAnimationProperties(image).cast(VIPS_FORMAT_UCHAR);
           image.heifsave(const_cast<char*>(baton->fileOut.data()), VImage::option()
             ->set("strip", !baton->withMetadata)
             ->set("Q", baton->heifQuality)
             ->set("compression", baton->heifCompression)
             ->set("effort", baton->heifEffort)
+            ->set("bitdepth", 8)
             ->set("subsample_mode", baton->heifChromaSubsampling == "4:4:4"
               ? VIPS_FOREIGN_SUBSAMPLE_OFF : VIPS_FOREIGN_SUBSAMPLE_ON)
             ->set("lossless", baton->heifLossless));
diff --git a/test/unit/avif.js b/test/unit/avif.js
index 9a17f7231..12ff888e0 100644
--- a/test/unit/avif.js
+++ b/test/unit/avif.js
@@ -103,4 +103,28 @@ describe('AVIF', () => {
       width: 10
     });
   });
+
+  it('should cast to uchar', async () => {
+    const data = await sharp(inputJpg)
+      .resize(32)
+      .sharpen()
+      .avif({ effort: 0 })
+      .toBuffer();
+    const { size, ...metadata } = await sharp(data)
+      .metadata();
+    assert.deepStrictEqual(metadata, {
+      channels: 3,
+      compression: 'av1',
+      depth: 'uchar',
+      format: 'heif',
+      hasAlpha: false,
+      hasProfile: false,
+      height: 26,
+      isProgressive: false,
+      pagePrimary: 0,
+      pages: 1,
+      space: 'srgb',
+      width: 32
+    });
+  });
 });