diff --git a/server/szurubooru/tests/assets/flv.flv b/server/szurubooru/tests/assets/flv.flv
new file mode 100644
index 00000000..799d137e
Binary files /dev/null and b/server/szurubooru/tests/assets/flv.flv differ
diff --git a/server/szurubooru/tests/func/test_mime.py b/server/szurubooru/tests/func/test_mime.py
index b33746b4..0c8f23d4 100644
--- a/server/szurubooru/tests/func/test_mime.py
+++ b/server/szurubooru/tests/func/test_mime.py
@@ -19,6 +19,7 @@ from szurubooru.func import mime
         ("heif.heif", "image/heif"),
         ("heic.heic", "image/heic"),
         ("heic-heix.heic", "image/heic"),
+        ("flv.flv", "video/x-flv"),
         ("text.txt", "application/octet-stream"),
     ],
 )
@@ -72,6 +73,8 @@ def test_is_flash(input_mime_type, expected_state):
         ("VIDEO/MP4", True),
         ("video/anything_else", False),
         ("application/ogg", True),
+        ("video/x-flv", True),
+        ("VIDEO/X-FLV", True),
         ("not a video", False),
     ],
 )
diff --git a/server/szurubooru/tests/func/test_posts.py b/server/szurubooru/tests/func/test_posts.py
index fa1b3bb6..4bd735a5 100644
--- a/server/szurubooru/tests/func/test_posts.py
+++ b/server/szurubooru/tests/func/test_posts.py
@@ -462,6 +462,13 @@ def test_update_post_source_with_too_long_string():
             model.Post.TYPE_FLASH,
             "1_244c8840887984c4.swf",
         ),
+        (
+            False,
+            "flv.flv",
+            "video/x-flv",
+            model.Post.TYPE_VIDEO,
+            "1_244c8840887984c4.flv",
+        ),
     ],
 )
 def test_update_post_content_for_new_post(