diff --git a/sig/nostr/crypto.rbs b/sig/nostr/crypto.rbs
index fb35a7e..9924f1c 100644
--- a/sig/nostr/crypto.rbs
+++ b/sig/nostr/crypto.rbs
@@ -1,6 +1,6 @@
 module Nostr
   class Crypto
-    BN_BASE: Integer
+    BN_BASE: 0 | 2 | 10 | 16
     CIPHER_CURVE: String
     CIPHER_ALGORITHM: String