diff --git a/src/index.ts b/src/index.ts
index 40098be..87281b8 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,5 @@
-import { ValidationError } from "./validation.ts";
-import { getLocaleById, localesSize } from "./repository/locales.ts";
+import { idIsValid, ValidationError } from "./validation.ts";
+import { getLocaleById } from "./repository/locales.ts";
 
 /**
  * Display the iconic Hello, World
@@ -8,10 +8,8 @@ export const sayHello = (id?: number) => {
   if (!id) {
     return;
   }
-  if (idInValidRange(id)) {
+  if (!idIsValid(id)) {
     throw new ValidationError(`Invalid index: ${id}`);
   }
   return getLocaleById(id);
 };
-
-const idInValidRange = (id: number) => id < 1 || id >= localesSize;
diff --git a/src/validation.ts b/src/validation.ts
index bdbb7a2..f3a52c9 100644
--- a/src/validation.ts
+++ b/src/validation.ts
@@ -4,4 +4,8 @@
  *
  @example * `throw new ValidationError("Bad id")`
  */
+import { localesSize } from "./repository/locales.ts";
+
 export class ValidationError extends Error {}
+
+export const idIsValid = (id: number) => id > 0 && id < localesSize;