diff --git a/lib/Cake/Model/Model.php b/lib/Cake/Model/Model.php
index 3a908f5df..4ae591015 100644
--- a/lib/Cake/Model/Model.php
+++ b/lib/Cake/Model/Model.php
@@ -3302,8 +3302,12 @@ class Model extends Object implements CakeEventListener {
  */
 	public function isUnique($fields, $or = true) {
 		if (is_array($or)) {
-			$isAssociative = count(array_filter(array_keys($or), 'is_string'));
-			if (!$isAssociative) {
+			$isRule = (
+				array_key_exists('rule', $or) &&
+				array_key_exists('required', $or) &&
+				array_key_exists('message', $or)
+			);
+			if (!$isRule) {
 				$args = func_get_args();
 				$fields = $args[1];
 				$or = isset($args[2]) ? $args[2] : true;
diff --git a/lib/Cake/Test/Case/Model/ModelValidationTest.php b/lib/Cake/Test/Case/Model/ModelValidationTest.php
index 270d61119..e25f87897 100644
--- a/lib/Cake/Test/Case/Model/ModelValidationTest.php
+++ b/lib/Cake/Test/Case/Model/ModelValidationTest.php
@@ -2450,7 +2450,7 @@ class ModelValidationTest extends BaseModelTest {
 	}
 
 /**
- * Test backward compatibility of the isUnique method when used as a validator for multiple fields.
+ * Test backward compatibility of the isUnique method when used as a validator for a single field.
  *
  * @return void
  */