diff --git a/src/br/cpf.spec.ts b/src/br/cpf.spec.ts
index a99f800f..e6b3c758 100644
--- a/src/br/cpf.spec.ts
+++ b/src/br/cpf.spec.ts
@@ -8,6 +8,12 @@ describe('br/cpf', () => {
     expect(result).toEqual('231.002.999-00');
   });
 
+  it('format: 216.957.050-09', () => {
+    const result = format('216.957.050-09');
+
+    expect(result).toEqual('216.957.050-09');
+  });
+
   it('validate:390.533.447-05', () => {
     const result = validate('390.533.447-05');
 
diff --git a/src/br/cpf.ts b/src/br/cpf.ts
index 51495f0d..48898e04 100644
--- a/src/br/cpf.ts
+++ b/src/br/cpf.ts
@@ -47,7 +47,11 @@ const impl: Validator = {
   format(input: string): string {
     const [value] = clean(input);
 
-    const [a, b, c, d] = strings.splitAt(value, 3, 6, input.length - 2);
+    if (value.length !== 11) {
+      throw new exceptions.InvalidLength('CPF must have 11 digits.');
+    }
+
+    const [a, b, c, d] = strings.splitAt(value, 3, 6, 9, 11);
 
     return `${a}.${b}.${c}-${d}`;
   },