diff --git a/flaskserver.py b/flaskserver.py
index 94eafd5..913d749 100644
--- a/flaskserver.py
+++ b/flaskserver.py
@@ -17,6 +17,10 @@
 
 
 def flask_server():
+    # python -O silently strips assert statements, so refuse to run unchecked
+    if not __debug__:
+        raise Exception('Refusing to run with assertions disabled (python -O)')
+
     # Load, verify, and cache server static key at startup
     # (Refuse to start if key non-existing or invalid)
     PINServerECDH.load_private_key()
diff --git a/pindb.py b/pindb.py
index bba3408..8957a37 100644
--- a/pindb.py
+++ b/pindb.py
@@ -180,7 +180,7 @@ def _load_pin_fields(cls, pin_pubkey_hash, pin_pubkey, aes_pin_data_key):
             assert version_bytes == version
         hmac_payload = hmac_sha256(pin_auth_key, version_bytes + encrypted)
 
-        assert hmac_payload == hmac_received
+        assert compare_digest(hmac_payload, hmac_received)
 
         storage_aes_key = hmac_sha256(aes_pin_data_key, pin_pubkey)
         plaintext = decrypt(storage_aes_key, encrypted)