diff --git a/src/Schema/Keywords/Nullable.php b/src/Schema/Keywords/Nullable.php
index 9569ac27..58dea829 100644
--- a/src/Schema/Keywords/Nullable.php
+++ b/src/Schema/Keywords/Nullable.php
@@ -27,6 +27,10 @@ public function validate($data, bool $nullable): void
 
     public function nullableByType(): bool
     {
-        return ! is_string($this->parentSchema->type) && in_array('null', $this->parentSchema->type);
+        if (is_string($this->parentSchema->type)) {
+            return $this->parentSchema->type === 'null';
+        }
+
+        return in_array('null', $this->parentSchema->type);
     }
 }
diff --git a/tests/Schema/Keywords/NullableTest.php b/tests/Schema/Keywords/NullableTest.php
index db9c8638..61c649cb 100644
--- a/tests/Schema/Keywords/NullableTest.php
+++ b/tests/Schema/Keywords/NullableTest.php
@@ -25,6 +25,20 @@ public function testItValidatesNullableGreen(): void
         $this->addToAssertionCount(1);
     }
 
+    public function testItValidatesNullableStandaloneGreen(): void
+    {
+        $spec = <<<SPEC
+schema:
+    type: 'null'
+SPEC;
+
+        $schema = $this->loadRawSchema($spec);
+        $data   = null;
+
+        (new SchemaValidator())->validate($data, $schema);
+        $this->addToAssertionCount(1);
+    }
+
     public function testItValidatesNullableRed(): void
     {
         $spec = <<<SPEC