diff --git a/src/Node/Expression/NullCoalesceExpression.php b/src/Node/Expression/NullCoalesceExpression.php
index 49326d467..917d31a3b 100644
--- a/src/Node/Expression/NullCoalesceExpression.php
+++ b/src/Node/Expression/NullCoalesceExpression.php
@@ -22,11 +22,15 @@ class NullCoalesceExpression extends ConditionalExpression
 {
     public function __construct(\Twig_NodeInterface $left, \Twig_NodeInterface $right, $lineno)
     {
-        $test = new AndBinary(
-            new DefinedTest(clone $left, 'defined', new Node(), $left->getTemplateLine()),
-            new NotUnary(new NullTest($left, 'null', new Node(), $left->getTemplateLine()), $left->getTemplateLine()),
-            $left->getTemplateLine()
-        );
+        $test = new DefinedTest(clone $left, 'defined', new Node(), $left->getTemplateLine());
+        // for "block()", we don't need the null test as the return value is always a string
+        if (!$left instanceof BlockReferenceExpression) {
+            $test = new AndBinary(
+                $test,
+                new NotUnary(new NullTest($left, 'null', new Node(), $left->getTemplateLine()), $left->getTemplateLine()),
+                $left->getTemplateLine()
+            );
+        }
 
         parent::__construct($test, $left, $right, $lineno);
     }
diff --git a/tests/Fixtures/tests/null_coalesce_block.test b/tests/Fixtures/tests/null_coalesce_block.test
new file mode 100644
index 000000000..73579140c
--- /dev/null
+++ b/tests/Fixtures/tests/null_coalesce_block.test
@@ -0,0 +1,9 @@
+--TEST--
+Twig supports the ?? operator with blocks
+--TEMPLATE--
+{% block foo %}OK{% endblock %}
+{{ block('foo') ?? 'KO' }}
+--DATA--
+return []
+--EXPECT--
+OKOK