diff --git a/event.ts b/event.ts
index dd05a6a..c9ee5c4 100644
--- a/event.ts
+++ b/event.ts
@@ -105,7 +105,7 @@ export function verifySignature(event: Event & {sig: string}): boolean {
   )
 }
 
-export function signEvent(event: Event, key: string): string {
+export function signEvent(event: UnsignedEvent, key: string): string {
   return secp256k1.utils.bytesToHex(
     secp256k1.schnorr.signSync(getEventHash(event), key)
   )