diff --git a/crates/node/src/node_implementations/geth.rs b/crates/node/src/node_implementations/geth.rs
index bc9ac8f..ac588fd 100644
--- a/crates/node/src/node_implementations/geth.rs
+++ b/crates/node/src/node_implementations/geth.rs
@@ -131,7 +131,11 @@ impl GethNode {
 	}
 
 	pub async fn new_existing(private_key: &str, rpc_port: u16) -> anyhow::Result<Self> {
-		use alloy::{primitives::FixedBytes, signers::local::PrivateKeySigner};
+		use alloy::{
+			primitives::FixedBytes,
+			providers::{Provider, ProviderBuilder},
+			signers::local::PrivateKeySigner,
+		};
 
 		let key_str = private_key.trim().strip_prefix("0x").unwrap_or(private_key.trim());
 		let key_bytes = alloy::hex::decode(key_str)
@@ -152,6 +156,13 @@ impl GethNode {
 
 		let address = signer.address();
 		let wallet = Arc::new(EthereumWallet::new(signer));
+		let connection_string = format!("http://localhost:{}", rpc_port);
+
+		let chain_id = ProviderBuilder::new()
+			.connect_http(connection_string.parse()?)
+			.get_chain_id()
+			.await
+			.context("Failed to query chain ID from RPC")?;
 
 		let node = Self {
 			connection_string: format!("http://localhost:{}", rpc_port),
@@ -160,7 +171,7 @@ impl GethNode {
 			logs_directory: PathBuf::new(),
 			geth: PathBuf::new(),
 			id: 0,
-			chain_id: 1337,
+			chain_id,
 			handle: None,
 			start_timeout: Duration::from_secs(0),
 			wallet,
@@ -174,6 +185,8 @@ impl GethNode {
 		Ok(node)
 	}
 
+	/// Ensure that the given address has at least 1000 ETH, funding it from the node's managed
+	/// account if necessary.
 	async fn ensure_funded(&self, address: Address) -> anyhow::Result<()> {
 		use alloy::{
 			primitives::utils::{format_ether, parse_ether},
diff --git a/crates/node/src/node_implementations/substrate.rs b/crates/node/src/node_implementations/substrate.rs
index 7c7dde6..51835de 100644
--- a/crates/node/src/node_implementations/substrate.rs
+++ b/crates/node/src/node_implementations/substrate.rs
@@ -80,6 +80,7 @@ pub struct SubstrateNode {
 	wallet: Arc<EthereumWallet>,
 	nonce_manager: CachedNonceManager,
 	provider: OnceCell<ConcreteProvider<ReviveNetwork, Arc<EthereumWallet>>>,
+	chain_id: alloy::primitives::ChainId,
 }
 
 impl SubstrateNode {
@@ -129,11 +130,16 @@ impl SubstrateNode {
 			wallet: wallet.clone(),
 			nonce_manager: Default::default(),
 			provider: Default::default(),
+			chain_id: CHAIN_ID,
 		}
 	}
 
 	pub async fn new_existing(private_key: &str, rpc_port: u16) -> anyhow::Result<Self> {
-		use alloy::{primitives::FixedBytes, signers::local::PrivateKeySigner};
+		use alloy::{
+			primitives::FixedBytes,
+			providers::{Provider, ProviderBuilder},
+			signers::local::PrivateKeySigner,
+		};
 
 		let key_str = private_key.trim().strip_prefix("0x").unwrap_or(private_key.trim());
 		let key_bytes = alloy::hex::decode(key_str)
@@ -153,13 +159,21 @@ impl SubstrateNode {
 			.map_err(|e| anyhow::anyhow!("Failed to create signer from private key: {}", e))?;
 
 		let wallet = Arc::new(EthereumWallet::new(signer));
+		let rpc_url = format!("http://localhost:{}", rpc_port);
+
+		// Query the chain ID from the RPC
+		let chain_id = ProviderBuilder::new()
+			.connect_http(rpc_url.parse()?)
+			.get_chain_id()
+			.await
+			.context("Failed to query chain ID from RPC")?;
 
 		Ok(Self {
 			id: 0,
 			node_binary: PathBuf::new(),
 			eth_proxy_binary: PathBuf::new(),
 			export_chainspec_command: String::new(),
-			rpc_url: format!("http://localhost:{}", rpc_port),
+			rpc_url,
 			base_directory: PathBuf::new(),
 			logs_directory: PathBuf::new(),
 			substrate_process: None,
@@ -167,6 +181,7 @@ impl SubstrateNode {
 			wallet,
 			nonce_manager: Default::default(),
 			provider: Default::default(),
+			chain_id,
 		})
 	}
 
@@ -383,7 +398,7 @@ impl SubstrateNode {
 				construct_concurrency_limited_provider::<ReviveNetwork, _>(
 					self.rpc_url.as_str(),
 					FallbackGasFiller::new(u64::MAX, 5_000_000_000, 1_000_000_000),
-					ChainIdFiller::new(Some(CHAIN_ID)),
+					ChainIdFiller::new(Some(self.chain_id)),
 					NonceFiller::new(self.nonce_manager.clone()),
 					self.wallet.clone(),
 				)