diff --git a/nobilis b/nobilis
index dfda74d..4e3c65d 160000
--- a/nobilis
+++ b/nobilis
@@ -1 +1 @@
-Subproject commit dfda74d1e4e2437a5027d0c62246129068f0d98d
+Subproject commit 4e3c65dcfe02bf985048d65c2ecd69705eaec38e
diff --git a/src/main/notifications.ts b/src/main/notifications.ts
index bd30b08..385484a 100644
--- a/src/main/notifications.ts
+++ b/src/main/notifications.ts
@@ -159,6 +159,14 @@ export class Notifier {
     if (starts(0x52, 0x49, 0x46, 0x46) && bytes.subarray(8, 12).toString() === 'WEBP') {
       return 'image/webp'
     }
+    // ISO-BMFF: AVIF and HEIC share the ftyp box four bytes in and are told
+    // apart by the brand after it. Only avif is claimed here - Chromium
+    // decodes that one and does not decode HEIC, so calling a HEIC file by
+    // its real name would promise a picture that never appears.
+    if (bytes.subarray(4, 8).toString() === 'ftyp') {
+      const brand = bytes.subarray(8, 12).toString()
+      if (brand === 'avif' || brand === 'avis') return 'image/avif'
+    }
     // Something else entirely. Chromium sniffs the bytes of an <img> either
     // way, so a wrong-but-plausible type still decodes what it can, and what
     // it cannot decode falls out of the null below rather than here.
diff --git a/src/renderer/src/components/MediaEmbed.tsx b/src/renderer/src/components/MediaEmbed.tsx
index dccabc7..fde12eb 100644
--- a/src/renderer/src/components/MediaEmbed.tsx
+++ b/src/renderer/src/components/MediaEmbed.tsx
@@ -225,7 +225,7 @@ export function MediaEmbed({
     // Browsers give no pause control over an animated GIF, so "don't autoplay"
     // is expressed by not loading it until asked.
     const animated =
-      attachment?.mimetype === 'image/gif' || /\.(gif|webp)(\?\S*)?$/i.test(fullSrc)
+      attachment?.mimetype === 'image/gif' || /\.(gif|webp|avif)(\?\S*)?$/i.test(fullSrc)
     if (animated && !autoplay && !playing) {
       return (
         <button type="button" className="media-embed paused" onClick={() => setPlaying(true)}>
diff --git a/src/renderer/src/lib/format.ts b/src/renderer/src/lib/format.ts
index 838cc6d..7e40c72 100644
--- a/src/renderer/src/lib/format.ts
+++ b/src/renderer/src/lib/format.ts
@@ -546,7 +546,7 @@ export function hostnameOf(url: string): string {
  */
 export const OPAQUE_IMAGE_HOSTS = ['i.ddos.lgbt']
 
-const IMAGE_EXT_RE = /\.(png|jpe?g|gif|webp|bmp)(\?\S*)?$/i
+const IMAGE_EXT_RE = /\.(png|jpe?g|gif|webp|bmp|avif)(\?\S*)?$/i
 const VIDEO_EXT_RE = /\.(mp4|webm|mov|mkv|ogv)(\?\S*)?$/i
 
 /**