diff --git a/packages/thirdweb/src/wallets/utils/normalizeChainId.test.ts b/packages/thirdweb/src/wallets/utils/normalizeChainId.test.ts
index 5c5af8acf57..b63fc4eaf46 100644
--- a/packages/thirdweb/src/wallets/utils/normalizeChainId.test.ts
+++ b/packages/thirdweb/src/wallets/utils/normalizeChainId.test.ts
@@ -17,4 +17,14 @@ describe("normalizeChainId", () => {
   it("should try to convert a string to a decimal (base 10) integer", () => {
     expect(normalizeChainId("1")).toBe(1);
   });
+
+  it("should reject invalid chain ids", () => {
+    expect(() => normalizeChainId("1abc")).toThrow("Invalid chain ID");
+    expect(() => normalizeChainId("abc")).toThrow("Invalid chain ID");
+    expect(() => normalizeChainId("0x")).toThrow("Invalid chain ID");
+    expect(() => normalizeChainId(Number.NaN)).toThrow("Invalid chain ID");
+    expect(() =>
+      normalizeChainId(BigInt(Number.MAX_SAFE_INTEGER) + 1n),
+    ).toThrow("Invalid chain ID");
+  });
 });
diff --git a/packages/thirdweb/src/wallets/utils/normalizeChainId.ts b/packages/thirdweb/src/wallets/utils/normalizeChainId.ts
index 6214d870fd3..9c3c2c224a6 100644
--- a/packages/thirdweb/src/wallets/utils/normalizeChainId.ts
+++ b/packages/thirdweb/src/wallets/utils/normalizeChainId.ts
@@ -4,14 +4,28 @@ import { hexToNumber, isHex } from "../../utils/encoding/hex.js";
  * @internal
  */
 export function normalizeChainId(chainId: string | number | bigint): number {
+  let normalizedChainId: number;
+
   if (typeof chainId === "number") {
-    return chainId;
-  }
-  if (isHex(chainId)) {
-    return hexToNumber(chainId);
+    normalizedChainId = chainId;
+  } else if (isHex(chainId)) {
+    normalizedChainId = hexToNumber(chainId);
+  } else if (typeof chainId === "bigint") {
+    if (chainId < 0n || chainId > BigInt(Number.MAX_SAFE_INTEGER)) {
+      throw new Error(`Invalid chain ID: ${chainId.toString()}`);
+    }
+    normalizedChainId = Number(chainId);
+  } else {
+    const trimmed = chainId.trim();
+    if (!/^\d+$/u.test(trimmed)) {
+      throw new Error(`Invalid chain ID: ${chainId}`);
+    }
+    normalizedChainId = Number.parseInt(trimmed, 10);
   }
-  if (typeof chainId === "bigint") {
-    return Number(chainId);
+
+  if (!Number.isSafeInteger(normalizedChainId) || normalizedChainId < 0) {
+    throw new Error(`Invalid chain ID: ${chainId.toString()}`);
   }
-  return Number.parseInt(chainId, 10);
+
+  return normalizedChainId;
 }