diff --git a/src/Capability/Discovery/SchemaGenerator.php b/src/Capability/Discovery/SchemaGenerator.php
index 6366fd49..04ee08f6 100644
--- a/src/Capability/Discovery/SchemaGenerator.php
+++ b/src/Capability/Discovery/SchemaGenerator.php
@@ -374,7 +374,8 @@ private function applyEnumConstraints(array $paramSchema, array $paramInfo): arr
 
             if ($jsonBackingType) {
                 if (isset($paramSchema['type']) && \is_array($paramSchema['type']) && \in_array('null', $paramSchema['type'])) {
-                    $paramSchema['type'] = ['null', $jsonBackingType];
+                    $paramSchema['type'] = [$jsonBackingType, 'null'];
+                    $paramSchema['enum'][] = null;
                 } else {
                     $paramSchema['type'] = $jsonBackingType;
                 }
@@ -383,7 +384,8 @@ private function applyEnumConstraints(array $paramSchema, array $paramInfo): arr
             // Non-backed enum - use names as enum values
             $paramSchema['enum'] = array_column($enumClass::cases(), 'name');
             if (isset($paramSchema['type']) && \is_array($paramSchema['type']) && \in_array('null', $paramSchema['type'])) {
-                $paramSchema['type'] = ['null', 'string'];
+                $paramSchema['type'] = ['string', 'null'];
+                $paramSchema['enum'][] = null;
             } else {
                 $paramSchema['type'] = 'string';
             }
diff --git a/tests/Unit/Capability/Discovery/SchemaGeneratorTest.php b/tests/Unit/Capability/Discovery/SchemaGeneratorTest.php
index 299e9854..c92121e6 100644
--- a/tests/Unit/Capability/Discovery/SchemaGeneratorTest.php
+++ b/tests/Unit/Capability/Discovery/SchemaGeneratorTest.php
@@ -197,7 +197,7 @@ public function testGeneratesCorrectSchemaForEnumParameters(): void
         $this->assertEquals(['type' => 'string', 'description' => 'Backed string enum', 'enum' => ['A', 'B']], $schema['properties']['stringEnum']);
         $this->assertEquals(['type' => 'integer', 'description' => 'Backed int enum', 'enum' => [1, 2]], $schema['properties']['intEnum']);
         $this->assertEquals(['type' => 'string', 'description' => 'Unit enum', 'enum' => ['Yes', 'No']], $schema['properties']['unitEnum']);
-        $this->assertEquals(['type' => ['null', 'string'], 'enum' => ['A', 'B'], 'default' => null], $schema['properties']['nullableEnum']);
+        $this->assertEquals(['type' => ['string', 'null'], 'enum' => ['A', 'B', null], 'default' => null], $schema['properties']['nullableEnum']);
         $this->assertEquals(['type' => 'integer', 'enum' => [1, 2], 'default' => 1], $schema['properties']['enumWithDefault']);
         $this->assertEqualsCanonicalizing(['stringEnum', 'intEnum', 'unitEnum'], $schema['required']);
     }