diff --git a/src/objectid.ts b/src/objectid.ts
index 13954071..e548aa81 100644
--- a/src/objectid.ts
+++ b/src/objectid.ts
@@ -4,9 +4,6 @@ import { type InspectFn, defaultInspect } from './parser/utils';
 import { ByteUtils } from './utils/byte_utils';
 import { NumberUtils } from './utils/number_utils';
 
-// Regular expression that checks for hex value
-const checkForHexRegExp = new RegExp('^[0-9a-fA-F]{24}$');
-
 // Unique sequence for the current process (initialized on first use)
 let PROCESS_UNIQUE: Uint8Array | null = null;
 
@@ -147,9 +144,23 @@ export class ObjectId extends BSONValue {
    * @internal
    * Validates the input string is a valid hex representation of an ObjectId.
    */
-  private static validateHexString(input: string): boolean {
-    if (input == null || input.length !== 24) return false;
-    return checkForHexRegExp.test(input);
+  private static validateHexString(string: string): boolean {
+    if (string?.length !== 24) return false;
+    for (let i = 0; i < 24; i++) {
+      const char = string.charCodeAt(i);
+      if (
+        // Check for ASCII 0-9
+        (char >= 48 && char <= 57) ||
+        // Check for ASCII a-f
+        (char >= 97 && char <= 102) ||
+        // Check for ASCII A-F
+        (char >= 65 && char <= 70)
+      ) {
+        continue;
+      }
+      return false;
+    }
+    return true;
   }
 
   /** Returns the ObjectId id as a 24 lowercase character hex string representation */