diff --git a/lib/marcel/mime_type/definitions.rb b/lib/marcel/mime_type/definitions.rb
index cd97e58..022a77f 100644
--- a/lib/marcel/mime_type/definitions.rb
+++ b/lib/marcel/mime_type/definitions.rb
@@ -37,6 +37,7 @@
 
 Marcel::MimeType.extend "application/x-x509-ca-cert", magic: [[0, '-----BEGIN CERTIFICATE-----']], extensions: %w( pem ), parents: "application/x-x509-cert;format=pem"
 
+Marcel::MimeType.extend "image/avif", magic: [[4, "ftypavif"]], extensions: %w( avif )
 Marcel::MimeType.extend "image/heif", magic: [[4, "ftypmif1"]], extensions: %w( heif )
 Marcel::MimeType.extend "image/heic", magic: [[4, "ftypheic"]], extensions: %w( heic )
 
diff --git a/test/fixtures/magic/image/avif/avif.avif b/test/fixtures/magic/image/avif/avif.avif
new file mode 100644
index 0000000..c357186
Binary files /dev/null and b/test/fixtures/magic/image/avif/avif.avif differ