diff --git a/src/lib/utils/passkey.ts b/src/lib/utils/passkey.ts
index 8feb6c7..a40fa0c 100644
--- a/src/lib/utils/passkey.ts
+++ b/src/lib/utils/passkey.ts
@@ -138,7 +138,11 @@ export const getCredentialOptions = ({
   // Enable PRF extension for zero-knowledge key derivation
   if (enablePRF) {
     options.publicKey.extensions = {
-      prf: {},
+      prf: {
+        eval: {
+          first: new TextEncoder().encode("ein-fortlaufender-32-byte-salt-"),
+        },
+      },
     };
   }