diff --git a/contrib/package/arch/PKGBUILD b/contrib/package/arch/PKGBUILD
index 51dc6bef..7535c9ec 100644
--- a/contrib/package/arch/PKGBUILD
+++ b/contrib/package/arch/PKGBUILD
@@ -9,6 +9,7 @@ license=('MIT')
 depends=("python" "lsof" "python-jinja")
 makedepends=("python-wheel" "python-setuptools" "python-build" "python-installer" "make" "pigz")
 optdepends=("ffmpeg: thumbnails for videos, images (slower) and audio, music tags"
+            "cfssl: generate TLS certificates on startup (pointless when reverse-proxied)"
             "python-mutagen: music tags (alternative)" 
             "python-pillow: thumbnails for images" 
             "python-pyvips: thumbnails for images (higher quality, faster, uses more ram)" 
diff --git a/contrib/package/nix/copyparty/default.nix b/contrib/package/nix/copyparty/default.nix
index 359b9d56..9380a1e5 100644
--- a/contrib/package/nix/copyparty/default.nix
+++ b/contrib/package/nix/copyparty/default.nix
@@ -3,6 +3,9 @@
 # use argon2id-hashed passwords in config files (sha2 is always available)
 withHashedPasswords ? true,
 
+# generate TLS certificates on startup (pointless when reverse-proxied)
+withCertgen ? false,
+
 # create thumbnails with Pillow; faster than FFmpeg / MediaProcessing
 withThumbnails ? true,
 
@@ -34,6 +37,7 @@ let
     ]
     ++ lib.optional withSMB impacket
     ++ lib.optional withFTPS pyopenssl
+    ++ lib.optional withCertgen cfssl
     ++ lib.optional withThumbnails pillow
     ++ lib.optional withFastThumbnails pyvips
     ++ lib.optional withMediaProcessing ffmpeg
diff --git a/copyparty/cert.py b/copyparty/cert.py
index 7ba0ca8e..6b40dea4 100644
--- a/copyparty/cert.py
+++ b/copyparty/cert.py
@@ -132,7 +132,10 @@ def _gen_srv(log: "RootLogger", args, netdevs: dict[str, Netdev]):
 
     try:
         expiry, inf = _read_crt(args, "srv.pem")
-        expired = time.time() + args.crt_sdays * 60 * 60 * 24 * 0.1 > expiry
+        if "sans" not in inf:
+            raise Exception("no useable cert found")
+
+        expired = time.time() + args.crt_sdays * 60 * 60 * 24 * 0.5 > expiry
         cert_insec = os.path.join(args.E.mod, "res/insecure.pem")
         for n in names:
             if n not in inf["sans"]: