diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 47bb8835e9..adf4ba2caa 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -19,6 +19,7 @@ Yii Framework 2 Change Log
 - Bug #18648: Fix `yii\web\Request` to properly handle HTTP Basic Auth headers (olegbaturin)
 - Enh #18726: Added `yii\helpers\Json::$prettyPrint` (rhertogh)
 - Enh #18734: Added `yii\validators\EmailValidator::$enableLocalIDN` (brandonkelly)
+- Bug #18756: Fix `\yii\validators\ExistValidator::queryValueExists` to validate against an array of unique values (DrDeath72)
 - Enh #18656: Added ability for `yii serve`'s `--router` param to take an alias (markhuot)
 - Bug #18274: Fix `yii\log\Logger` to calculate profile timings no matter the value of the flush interval (bizley)
 
diff --git a/framework/validators/ExistValidator.php b/framework/validators/ExistValidator.php
index eb86088d31..fb0761e1f8 100644
--- a/framework/validators/ExistValidator.php
+++ b/framework/validators/ExistValidator.php
@@ -280,7 +280,7 @@ class ExistValidator extends Validator
     private function queryValueExists($query, $value)
     {
         if (is_array($value)) {
-            return $query->count("DISTINCT [[$this->targetAttribute]]") == count($value) ;
+            return $query->count("DISTINCT [[$this->targetAttribute]]") == count(array_unique($value)) ;
         }
         return $query->exists();
     }
diff --git a/tests/framework/validators/ExistValidatorTest.php b/tests/framework/validators/ExistValidatorTest.php
index 472c74e6b1..45759d9016 100644
--- a/tests/framework/validators/ExistValidatorTest.php
+++ b/tests/framework/validators/ExistValidatorTest.php
@@ -97,6 +97,13 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         $m->test_val = [2, 3, 4, 5];
         $val->validateAttribute($m, 'test_val');
         $this->assertFalse($m->hasErrors('test_val'));
+        // existing non-unique array
+        $val = new ExistValidator(['targetAttribute' => 'ref']);
+        $val->allowArray = true;
+        $m = new ValidatorTestRefModel();
+        $m->test_val = [2, 2, 3, 3, 4, 4, 5, 5];
+        $val->validateAttribute($m, 'test_val');
+        $this->assertFalse($m->hasErrors('test_val'));
         // non-existing array
         $val = new ExistValidator(['targetAttribute' => 'ref']);
         $val->allowArray = true;