diff --git a/frontend/src/contracts.ts b/frontend/src/contracts.ts
index 0c5f904..c7d06c8 100644
--- a/frontend/src/contracts.ts
+++ b/frontend/src/contracts.ts
@@ -5,7 +5,7 @@ import { type MessageBox, MessageBox__factory } from '@oasisprotocol/demo-starte
 export type { MessageBox } from '@oasisprotocol/demo-starter-backend';
 
 import { useEthereumStore } from './stores/ethereum';
-import { VoidSigner } from 'ethers';
+import { type ContractRunner, VoidSigner } from 'ethers';
 
 const addr = import.meta.env.VITE_MESSAGE_BOX_ADDR!;
 
@@ -23,7 +23,7 @@ export function useMessageBox(): ComputedRef<MessageBox | null> {
       return null;
     }
 
-    return MessageBox__factory.connect(addr, eth.signer);
+    return MessageBox__factory.connect(addr, eth.signer as ContractRunner);
   });
 }
 
diff --git a/frontend/src/stores/ethereum.ts b/frontend/src/stores/ethereum.ts
index 0844dc3..e72e0fc 100644
--- a/frontend/src/stores/ethereum.ts
+++ b/frontend/src/stores/ethereum.ts
@@ -61,7 +61,7 @@ export function networkName(network?: Network): string {
 
 declare global {
   interface Window {
-    ethereum?: BrowserProvider & Eip1193Provider & sapphire.SapphireAnnex;
+    ethereum: BrowserProvider & Eip1193Provider & sapphire.SapphireAnnex;
   }
 }
 
@@ -91,7 +91,7 @@ export const useEthereumStore = defineStore('ethereum', () => {
       throw new MetaMaskNotInstalledError('MetaMask not installed!');
     }
 
-    return ethProvider;
+    return ethProvider as unknown as typeof window.ethereum;
   }
 
   async function init(addr: string, eth: Eip1193Provider) {