diff --git a/app/assets/javascripts/discourse/app/lib/uploads.js b/app/assets/javascripts/discourse/app/lib/uploads.js
index 95dbeba100b..a31095572e9 100644
--- a/app/assets/javascripts/discourse/app/lib/uploads.js
+++ b/app/assets/javascripts/discourse/app/lib/uploads.js
@@ -196,7 +196,7 @@ export function authorizedExtensions(staff, siteSettings) {
 
 function authorizedImagesExtensions(staff, siteSettings) {
   return authorizesAllExtensions(staff, siteSettings)
-    ? "png, jpg, jpeg, gif, svg, ico, heic, heif, webp"
+    ? "png, jpg, jpeg, gif, svg, ico, heic, heif, webp, avif"
     : imagesExtensions(staff, siteSettings).join(", ");
 }
 
@@ -230,7 +230,7 @@ export function authorizesOneOrMoreImageExtensions(staff, siteSettings) {
 }
 
 export function isImage(path) {
-  return /\.(png|webp|jpe?g|gif|svg|ico|heic|heif)$/i.test(path);
+  return /\.(png|webp|jpe?g|gif|svg|ico|heic|heif|avif)$/i.test(path);
 }
 
 export function isVideo(path) {
diff --git a/app/assets/javascripts/discourse/tests/unit/lib/uploads-test.js b/app/assets/javascripts/discourse/tests/unit/lib/uploads-test.js
index bede514d279..815e913001b 100644
--- a/app/assets/javascripts/discourse/tests/unit/lib/uploads-test.js
+++ b/app/assets/javascripts/discourse/tests/unit/lib/uploads-test.js
@@ -236,14 +236,16 @@ module("Unit | Utility | uploads", function (hooks) {
   });
 
   test("isImage", function (assert) {
-    ["png", "webp", "jpg", "jpeg", "gif", "ico"].forEach((extension) => {
-      let image = "image." + extension;
-      assert.ok(isImage(image), image + " is recognized as an image");
-      assert.ok(
-        isImage("http://foo.bar/path/to/" + image),
-        image + " is recognized as an image"
-      );
-    });
+    ["png", "webp", "jpg", "jpeg", "gif", "ico", "avif"].forEach(
+      (extension) => {
+        let image = "image." + extension;
+        assert.ok(isImage(image), image + " is recognized as an image");
+        assert.ok(
+          isImage("http://foo.bar/path/to/" + image),
+          image + " is recognized as an image"
+        );
+      }
+    );
     assert.notOk(isImage("file.txt"));
     assert.notOk(isImage("http://foo.bar/path/to/file.txt"));
     assert.notOk(isImage(""));
diff --git a/app/models/optimized_image.rb b/app/models/optimized_image.rb
index 25dd5b860a0..ec1827e36c6 100644
--- a/app/models/optimized_image.rb
+++ b/app/models/optimized_image.rb
@@ -175,7 +175,7 @@ class OptimizedImage < ActiveRecord::Base
     paths.each { |path| raise Discourse::InvalidAccess unless safe_path?(path) }
   end
 
-  IM_DECODERS ||= /\A(jpe?g|png|ico|gif|webp)\z/i
+  IM_DECODERS ||= /\A(jpe?g|png|ico|gif|webp|avif)\z/i
 
   def self.prepend_decoder!(path, ext_path = nil, opts = nil)
     opts ||= {}
diff --git a/config/nginx.sample.conf b/config/nginx.sample.conf
index c1a327fb76d..98a4b2dbbcc 100644
--- a/config/nginx.sample.conf
+++ b/config/nginx.sample.conf
@@ -203,7 +203,7 @@ server {
           try_files $uri =404;
       }
       # this allows us to bypass rails
-      location ~* \.(gif|png|jpg|jpeg|bmp|tif|tiff|ico|webp)$ {
+      location ~* \.(gif|png|jpg|jpeg|bmp|tif|tiff|ico||avif)$ {
           add_header Access-Control-Allow-Origin *;
           try_files $uri =404;
       }
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 51f8bb2cdb7..98ff694b03c 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -1352,12 +1352,12 @@ files:
     default: 50000
     max: 1024000
   theme_authorized_extensions:
-    default: "wasm|jpg|jpeg|png|woff|woff2|svg|eot|ttf|otf|gif|webp|js"
+    default: "wasm|jpg|jpeg|png|woff|woff2|svg|eot|ttf|otf|gif|webp|avif|js"
     type: list
     list_type: compact
   authorized_extensions:
     client: true
-    default: "jpg|jpeg|png|gif|heic|heif|webp"
+    default: "jpg|jpeg|png|gif|heic|heif|webp|avif"
     refresh: true
     type: list
     list_type: compact
diff --git a/lib/file_helper.rb b/lib/file_helper.rb
index aeab06d2900..229705fdd70 100644
--- a/lib/file_helper.rb
+++ b/lib/file_helper.rb
@@ -158,7 +158,7 @@ class FileHelper
   end
 
   def self.supported_images
-    @@supported_images ||= Set.new %w[jpg jpeg png gif svg ico webp]
+    @@supported_images ||= Set.new %w[jpg jpeg png gif svg ico webp avif]
   end
 
   def self.inline_images
diff --git a/lib/upload_creator.rb b/lib/upload_creator.rb
index 25d0284e2df..61ee801420a 100644
--- a/lib/upload_creator.rb
+++ b/lib/upload_creator.rb
@@ -662,7 +662,7 @@ class UploadCreator
         if is_animated != nil
           # FastImage will return nil if it cannot determine if animated
           is_animated
-        elsif type == "gif" || type == "webp"
+        elsif %w[gif webp avif].include?(type)
           # Only GIFs, WEBPs and a few other unsupported image types can be animated
           OptimizedImage.ensure_safe_paths!(@file.path)