diff --git a/packages/arb-ts/README.md b/packages/arb-ts/README.md
index 737c536e8d..8008929bf8 100644
--- a/packages/arb-ts/README.md
+++ b/packages/arb-ts/README.md
@@ -46,6 +46,8 @@ Bridging new a token to L2 (i.e., deploying a new token contract) through the st
 
 1. Set `PRIVKEY` environmental variable (you can use .env) to the key of the account from which you'll be deploying (account should have some balance of the token you're bridging).
 
+1. Set MAINNET_RPC environmental variable to L1 RPC endpoint (i.e., https://mainnet.infura.io/v3/my-infura-key)
+
 1. `yarn bridgeStandardToken`
 
 Required CL params:
diff --git a/packages/arb-ts/scripts/instantiate_bridge.ts b/packages/arb-ts/scripts/instantiate_bridge.ts
index 21e67e27a8..e6652836ab 100644
--- a/packages/arb-ts/scripts/instantiate_bridge.ts
+++ b/packages/arb-ts/scripts/instantiate_bridge.ts
@@ -66,7 +66,14 @@ export const instantiateBridge = async (
     : network
   const l2Network = networks[l1Network.partnerChainID]
 
+  if (!l1Network.rpcURL) {
+    throw new Error('L1 rpc url not set (see .env.sample or networks.ts)')
+  }
+  if (!l2Network.rpcURL) {
+    throw new Error('L2 rpc url not set (see .env.sample or networks.ts)')
+  }
   const ethProvider = new JsonRpcProvider(l1Network.rpcURL)
+
   const arbProvider = new JsonRpcProvider(l2Network.rpcURL)
 
   const l1Signer = (() => {