diff --git a/src/async.test.ts b/src/async.test.ts
index 395a054e..af315cb8 100644
--- a/src/async.test.ts
+++ b/src/async.test.ts
@@ -27,6 +27,7 @@ test("evm coin name", async () => {
   expect(coder.coinType).toBe(2147483658);
   expect(coder.name).toBe("op");
   expect(coder.evmChainId).toBe(10);
+  expect("isUnknownChain" in coder).toBeFalse();
 });
 
 test("evm coin type", async () => {
@@ -34,6 +35,15 @@ test("evm coin type", async () => {
   expect(coder.coinType).toBe(2147483658);
   expect(coder.name).toBe("op");
   expect(coder.evmChainId).toBe(10);
+  expect(coder.isUnknownChain).toBeFalse();
+});
+
+test("unknown evm coin type", async () => {
+  const coder = await getCoderByCoinTypeAsync(2147483659);
+  expect(coder.coinType).toBe(2147483659);
+  expect(coder.name).toBe("Unknown Chain (11)");
+  expect(coder.evmChainId).toBe(11);
+  expect(coder.isUnknownChain).toBeTrue();
 });
 
 const nonEvmCoinNames = Object.keys(nonEvmCoinNameToTypeMap);
diff --git a/src/async.ts b/src/async.ts
index 36825468..b1000d57 100644
--- a/src/async.ts
+++ b/src/async.ts
@@ -46,24 +46,24 @@ export const getCoderByCoinTypeAsync = async <
   const names =
     coinTypeToNameMap[String(coinType) as keyof typeof coinTypeToNameMap];
 
-  if (!names) throw new Error(`Unsupported coin type: ${coinType}`);
-
-  const [name] = names;
-
   if (coinType >= SLIP44_MSB) {
     // EVM coin
     const evmChainId = coinTypeToEvmChainId(coinType);
+    const isUnknownChain = !names;
+    const name = isUnknownChain ? `Unknown Chain (${evmChainId})` : names[0];
     return {
       name,
       coinType: coinType as EvmCoinType,
       evmChainId,
+      isUnknownChain,
       encode: eth.encode,
       decode: eth.decode,
     } as GetCoderByCoinType<TCoinType>;
   }
-  const mod = await import(`./coin/${name}`);
 
+  if (!names) throw new Error(`Unsupported coin type: ${coinType}`);
+  const [name] = names;
+  const mod = await import(`./coin/${name}`);
   if (!mod) throw new Error(`Failed to load coin: ${name}`);
-
   return mod[name];
 };
diff --git a/src/index.test.ts b/src/index.test.ts
index af086f3a..33eb731a 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -31,6 +31,7 @@ test("evm coin name", () => {
   expect(coder.coinType).toBe(2147483658);
   expect(coder.name).toBe("op");
   expect(coder.evmChainId).toBe(10);
+  expect("isUnknownChain" in coder).toBeFalse();
   expect(coder.encode).toBeFunction();
   expect(coder.decode).toBeFunction();
 });
@@ -40,6 +41,7 @@ test("evm coin type", () => {
   expect(coder.coinType).toBe(2147483658);
   expect(coder.name).toBe("op");
   expect(coder.evmChainId).toBe(10);
+  expect(coder.isUnknownChain).toBeFalse();
   expect(coder.encode).toBeFunction();
   expect(coder.decode).toBeFunction();
 });
diff --git a/src/index.ts b/src/index.ts
index 1f2bb8ab..07b51a65 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -73,6 +73,7 @@ export const getCoderByCoinType = <
   const names =
     coinTypeToNameMap[String(coinType) as keyof typeof coinTypeToNameMap];
   // https://docs.ens.domains/ens-improvement-proposals/ensip-11-evmchain-address-resolution
+
   if (coinType >= SLIP44_MSB) {
     // EVM coin
     const evmChainId = coinTypeToEvmChainId(coinType);
@@ -87,12 +88,12 @@ export const getCoderByCoinType = <
       encode: ethFormat.encode,
       decode: ethFormat.decode,
     } as GetCoderByCoinType<TCoinType>;
-  } else {
-    if (!names) {
-      throw new Error(`Unsupported coin type: ${coinType}`);
-    }
-    const [name] = names;
-    const format = formats[name as keyof typeof formats];
-    return format as GetCoderByCoinType<TCoinType>;
   }
+
+  if (!names) {
+    throw new Error(`Unsupported coin type: ${coinType}`);
+  }
+  const [name] = names;
+  const format = formats[name as keyof typeof formats];
+  return format as GetCoderByCoinType<TCoinType>;
 };
diff --git a/src/types.ts b/src/types.ts
index 3f68f198..0b36d7c8 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -26,7 +26,9 @@ export type CoinTypeToFormatMap = {
     : never;
 };
 export type CoinNameToFormatMap = {
-  [key in CoinName]: CoinTypeToFormatMap[CoinNameToTypeMap[key]];
+  [key in CoinName]: Prettify<
+    Omit<CoinTypeToFormatMap[CoinNameToTypeMap[key]], "isUnknownChain">
+  >;
 };
 
 export type EvmCoinMap = typeof evmCoinNameToTypeMap;