diff --git a/src/Assert.php b/src/Assert.php
index 5451fe1..5853614 100644
--- a/src/Assert.php
+++ b/src/Assert.php
@@ -1822,11 +1822,24 @@ public static function countBetween($array, $min, $max, $message = '')
      */
     public static function isList($array, $message = '')
     {
-        if (!\is_array($array) || $array !== \array_values($array)) {
+        if (!\is_array($array)) {
             static::reportInvalidArgument(
                 $message ?: 'Expected list - non-associative array.'
             );
         }
+
+        if ($array === \array_values($array)) {
+            return;
+        }
+
+        $nextKey = -1;
+        foreach ($array as $k => $v) {
+            if ($k !== ++$nextKey) {
+                static::reportInvalidArgument(
+                    $message ?: 'Expected list - non-associative array.'
+                );
+            }
+        }
     }
 
     /**
diff --git a/tests/AssertTest.php b/tests/AssertTest.php
index 9565909..db3b421 100644
--- a/tests/AssertTest.php
+++ b/tests/AssertTest.php
@@ -51,6 +51,12 @@ public function getTests()
     {
         $resource = self::getResource();
 
+        $nanList = array('key' => 2, NAN);
+        unset($nanList['key']);
+
+        $normalList = array('foo' => 'b', 3);
+        unset($normalList['foo']);
+
         return array(
             array('string', array('value'), true),
             array('string', array(''), true),
@@ -495,6 +501,8 @@ public function getTests()
             array('isList', array(array(false)), true),
             array('isList', array(array(array(1), array(2))), true),
             array('isList', array(array(array('foo' => 'bar'), array('baz' => 'tab'))), true),
+            array('isList', array($nanList), true),
+            array('isList', array($normalList), true),
             array('isNonEmptyList', array(array(1, 2, 3)), true),
             array('isNonEmptyList', array(array()), false),
             array('isNonEmptyList', array(array(0 => 1, 2 => 3)), false),