diff --git a/src/decorator/array/ArrayUnique.ts b/src/decorator/array/ArrayUnique.ts
index 0979aeefc0..98d00efeaa 100644
--- a/src/decorator/array/ArrayUnique.ts
+++ b/src/decorator/array/ArrayUnique.ts
@@ -12,7 +12,7 @@ export function arrayUnique(array: unknown[], identifier?: ArrayUniqueIdentifier
   if (!Array.isArray(array)) return false;
 
   if (identifier) {
-    array = array.map(o => (o != null ? identifier(o) : o));
+    array = array.flatMap(o => (o != null ? identifier(o) : o));
   }
 
   const uniqueItems = array.filter((a, b, c) => c.indexOf(a) === b);
diff --git a/test/functional/validation-functions-and-decorators.spec.ts b/test/functional/validation-functions-and-decorators.spec.ts
index 5144a0db48..b781d4b137 100644
--- a/test/functional/validation-functions-and-decorators.spec.ts
+++ b/test/functional/validation-functions-and-decorators.spec.ts
@@ -4610,6 +4610,51 @@ describe('ArrayUnique with identifier', () => {
   });
 });
 
+describe('ArrayUnique with array return values', () => {
+  const identifier = o => o.name;
+  const validValues = [
+    [['world'], ['hello'], ['superman']],
+    [['world', 'superman'], ['hello']],
+    [['superman', 'world', 'hello']],
+    [['1'], ['2'], [null], [undefined]],
+  ].map(list => list.map(name => ({ name })));
+  const invalidValues: any[] = [
+    null,
+    undefined,
+    [['world'], ['hello'], ['hello']],
+    [['world'], ['hello', 'hello']],
+    [['world', 'hello'], ['world']],
+    [['1'], ['1'], ['1']],
+  ].map(list => list?.map(name => (name != null ? { name } : name)));
+
+  class MyClass {
+    @ArrayUnique(identifier)
+    someProperty: { name: string }[];
+  }
+
+  it('should not fail if validator.validate said that its valid', () => {
+    return checkValidValues(new MyClass(), validValues);
+  });
+
+  it('should fail if validator.validate said that its invalid', () => {
+    return checkInvalidValues(new MyClass(), invalidValues);
+  });
+
+  it('should not fail if method in validator said that its valid', () => {
+    validValues.forEach(value => expect(arrayUnique(value, identifier)).toBeTruthy());
+  });
+
+  it('should fail if method in validator said that its invalid', () => {
+    invalidValues.forEach(value => expect(arrayUnique(value, identifier)).toBeFalsy());
+  });
+
+  it('should return error object with proper data', () => {
+    const validationType = 'arrayUnique';
+    const message = "All someProperty's elements must be unique";
+    return checkReturnedError(new MyClass(), invalidValues, validationType, message);
+  });
+});
+
 describe('isInstance', () => {
   class MySubClass {
     // Empty