diff --git a/.changeset/early-toes-fly.md b/.changeset/early-toes-fly.md
new file mode 100644
index 0000000..1e42fd0
--- /dev/null
+++ b/.changeset/early-toes-fly.md
@@ -0,0 +1,5 @@
+---
+"@coinbase-platform/paymaster": patch
+---
+
+fix(paymaster): use `string` for nonce in user operation
diff --git a/packages/paymaster/src/rpc.ts b/packages/paymaster/src/rpc.ts
index 4009d05..13e4bd1 100644
--- a/packages/paymaster/src/rpc.ts
+++ b/packages/paymaster/src/rpc.ts
@@ -156,7 +156,7 @@ export type RpcRequestConfig =
 
 type UserOperation = {
   sender: string;
-  nonce: number;
+  nonce: string;
   initCode: string;
   callData: string;
   callGasLimit: string;