diff --git a/links/file_views.py b/links/file_views.py
index 2a03253..c9de923 100644
--- a/links/file_views.py
+++ b/links/file_views.py
@@ -74,7 +74,15 @@ def _save_uploaded_file(f):
 
     os.rename(tmp_path, dest_path)
 
-    mime_type = f.content_type or mimetypes.guess_type(f.name)[0] or 'application/octet-stream'
+    guessed = mimetypes.guess_type(f.name)[0]
+    # Clients (notably the iOS uploader) often send a generic
+    # "application/octet-stream" Content-Type even for media files. When that
+    # happens, prefer the type inferred from the filename extension so the
+    # file is previewable/streamable in the UI.
+    if f.content_type and f.content_type != 'application/octet-stream':
+        mime_type = f.content_type
+    else:
+        mime_type = guessed or f.content_type or 'application/octet-stream'
     return FileUpload.objects.create(
         name=f.name,
         stored_name=stored_name,
diff --git a/tests/test_files_api.py b/tests/test_files_api.py
index 094bbf4..c949505 100644
--- a/tests/test_files_api.py
+++ b/tests/test_files_api.py
@@ -27,6 +27,21 @@ def _pdf():
     return SimpleUploadedFile("document.pdf", data, content_type="application/pdf")
 
 
+def _mp4_generic_content_type():
+    """An .mp4 upload whose client sent a generic Content-Type.
+
+    Reproduces the iOS-uploader behaviour that caused mb4 files to be
+    persisted as "application/octet-stream" and therefore un-previewable
+    in the UI. The server must infer "video/mp4" from the filename instead.
+    """
+    # minimal mp4 box header — content is irrelevant, only the extension
+    # and Content-Type matter for the mime-type inference path.
+    data = b"\x00\x00\x00\x20ftypisom\x00\x00\x02\x00isomiso2avc1mp41"
+    return SimpleUploadedFile(
+        "clip.mp4", data, content_type="application/octet-stream"
+    )
+
+
 @pytest.mark.django_db
 class TestFilesAPI:
     BASE = "/api/files"
@@ -171,3 +186,21 @@ class TestFilesAPI:
         ).json()[0]
         assert "formatted_size" in uploaded
         assert "B" in uploaded["formatted_size"]
+
+    def test_upload_infers_mime_from_filename_when_client_sends_generic(self, api_client):
+        """An .mp4 uploaded with Content-Type=application/octet-stream must
+        still be persisted as video/mp4 so the UI can render a <video>."""
+        uploaded = api_client.post(
+            f"{self.BASE}", {"files": _mp4_generic_content_type()}, format="multipart"
+        ).json()[0]
+        assert uploaded["mime_type"] == "video/mp4"
+
+    def test_download_serves_inline_for_generic_content_type_mp4(self, client, api_client):
+        uploaded = api_client.post(
+            f"{self.BASE}", {"files": _mp4_generic_content_type()}, format="multipart"
+        ).json()[0]
+        pk, name = uploaded["id"], uploaded["name"]
+        r = client.get(f"/ui/files/{pk}-{name}")
+        assert r.status_code == 200
+        assert r["Content-Type"] == "video/mp4"
+        assert (r["Content-Disposition"] or "").startswith("inline"), r["Content-Disposition"]