diff --git a/doc/filters/map.rst b/doc/filters/map.rst
index 1083bfe5eae..c165bd3ea93 100644
--- a/doc/filters/map.rst
+++ b/doc/filters/map.rst
@@ -23,7 +23,7 @@ The arrow function also receives the key as a second argument:
         "Alice": "Dupond",
     } %}
 
-    {{ people|map((last, first) => "#{first} #{last}")|join(', ') }}
+    {{ people|map((value, key) => "#{value} #{key}")|join(', ') }}
     {# outputs Bob Smith, Alice Dupond #}
 
 Note that the arrow function has access to the current context.
diff --git a/src/Extension/CoreExtension.php b/src/Extension/CoreExtension.php
index fd6e1c22885..c2c04e95ef4 100644
--- a/src/Extension/CoreExtension.php
+++ b/src/Extension/CoreExtension.php
@@ -543,6 +543,8 @@ function twig_replace_filter($str, $from)
  */
 function twig_round($value, $precision = 0, $method = 'common')
 {
+    $value = (float) $value;
+
     if ('common' === $method) {
         return round($value, $precision);
     }
@@ -551,8 +553,6 @@ function twig_round($value, $precision = 0, $method = 'common')
         throw new RuntimeError('The round filter only supports the "common", "ceil", and "floor" methods.');
     }
 
-    $value = (float) $value;
-
     return $method($value * 10 ** $precision) / 10 ** $precision;
 }
 
diff --git a/tests/Fixtures/filters/round.test b/tests/Fixtures/filters/round.test
index bb6afcf417d..264b230d19f 100644
--- a/tests/Fixtures/filters/round.test
+++ b/tests/Fixtures/filters/round.test
@@ -13,6 +13,8 @@
 
 {{ ''|round(-1, 'floor')}}
 {{ null|round(-1, 'floor')}}
+{{ null|round }}
+{{ null|round(2, 'ceil') }}
 --DATA--
 return []
 --EXPECT--
@@ -28,3 +30,5 @@ return []
 
 0
 0
+0
+0