diff --git a/README.md b/README.md
index 6548b2d..2e8ce86 100644
--- a/README.md
+++ b/README.md
@@ -40,7 +40,6 @@ $event = new CloudEvent(
     id: uniqid(),
     subject: 'user-123',
     time: CloudEvent::now(),
-    datacontenttype: 'application/json',
     data: [
         'userId' => '123',
         'email' => 'user@example.com',
@@ -49,7 +48,7 @@ $event = new CloudEvent(
 );
 ```
 
-When using the constructor, only `type`, `source` and `id` are required. All other attributes are optional. Arrays passed to `CloudEvent::fromArray()` must also carry an explicit `specversion`.
+When using the constructor, only `type`, `source` and `id` are required. All other attributes are optional. `datacontenttype` defaults to `application/json`; pass `null` to leave it unset. Arrays passed to `CloudEvent::fromArray()` must also carry an explicit `specversion`.
 
 `CloudEvent::now()` returns the current time as an RFC 3339 UTC timestamp with millisecond precision (e.g., `2025-11-07T10:00:00.123Z`), ready to use as the `time` attribute.
 
@@ -136,7 +135,7 @@ The `CloudEvent` class supports the following context attributes according to th
 - **source** (required): URI-reference identifying the context in which the event happened (e.g., "https://example.com/user-service")
 - **specversion** (required): CloudEvents specification version (default: "1.0")
 - **type** (required): Event type identifier, ideally reverse-DNS prefixed (e.g., "com.example.user.created")
-- **datacontenttype** (optional): RFC 2046 content type of the data field (e.g., "application/json")
+- **datacontenttype** (optional): RFC 2046 content type of the data field (constructor default: "application/json")
 - **dataschema** (optional): URI identifying the schema that data adheres to
 - **subject** (optional): Subject of the event in the context of the source
 - **time** (optional): Timestamp of when the occurrence happened (RFC 3339 format)
diff --git a/src/CloudEvents/CloudEvent.php b/src/CloudEvents/CloudEvent.php
index 71bd6b5..7da33da 100644
--- a/src/CloudEvents/CloudEvent.php
+++ b/src/CloudEvents/CloudEvent.php
@@ -46,7 +46,7 @@ class CloudEvent
      * @param string $specversion CloudEvents spec version (default: "1.0")
      * @param string|null $subject Optional subject of the event in the context of the source
      * @param string|null $time Optional event timestamp in RFC 3339 format
-     * @param string|null $datacontenttype Optional content type of data (RFC 2046, e.g., "application/json")
+     * @param string|null $datacontenttype Content type of data (RFC 2046, default: "application/json"); pass null to leave it unset
      * @param mixed $data Optional event payload of any type
      * @param string|null $dataschema Optional URI identifying the schema that data adheres to
      * @param array<string, mixed> $extensions Extension attributes (lowercase alphanumeric names, boolean/integer/string values)
@@ -58,7 +58,7 @@ public function __construct(
         public readonly string $specversion = '1.0',
         public readonly ?string $subject = null,
         public readonly ?string $time = null,
-        public readonly ?string $datacontenttype = null,
+        public readonly ?string $datacontenttype = 'application/json',
         public readonly mixed $data = null,
         public readonly ?string $dataschema = null,
         public readonly array $extensions = []
@@ -81,6 +81,11 @@ public static function now(): string
     /**
      * Create CloudEvent from array
      *
+     * Unlike the constructor, datacontenttype is not defaulted here: a
+     * parsed event keeps the wire form, so an absent attribute stays
+     * absent (per the JSON format, absent datacontenttype already
+     * implies a JSON payload).
+     *
      * @param array<string, mixed> $array
      * @return self
      * @throws InvalidArgumentException
diff --git a/tests/CloudEvents/CloudEventTest.php b/tests/CloudEvents/CloudEventTest.php
index cb56aeb..662a49b 100644
--- a/tests/CloudEvents/CloudEventTest.php
+++ b/tests/CloudEvents/CloudEventTest.php
@@ -45,10 +45,23 @@ public function testConstructorWithDefaults(): void
         $this->assertNull($event->subject);
         $this->assertEquals('test-id', $event->id);
         $this->assertNull($event->time);
-        $this->assertNull($event->datacontenttype);
+        $this->assertEquals('application/json', $event->datacontenttype);
         $this->assertNull($event->data);
     }
 
+    public function testDatacontenttypeAllowsExplicitNull(): void
+    {
+        $event = new CloudEvent(
+            type: 'test.event',
+            source: 'test-service',
+            id: 'test-id',
+            datacontenttype: null
+        );
+
+        $this->assertNull($event->datacontenttype);
+        $this->assertArrayNotHasKey('datacontenttype', $event->toArray());
+    }
+
     public function testFromArray(): void
     {
         $data = [
@@ -228,11 +241,11 @@ public function testToArrayOmitsAbsentOptionalAttributes(): void
             'specversion' => '1.0',
             'type' => 'test.event',
             'source' => 'test-service',
-            'id' => 'test-id'
+            'id' => 'test-id',
+            'datacontenttype' => 'application/json'
         ], $array);
         $this->assertArrayNotHasKey('subject', $array);
         $this->assertArrayNotHasKey('time', $array);
-        $this->assertArrayNotHasKey('datacontenttype', $array);
         $this->assertArrayNotHasKey('data', $array);
     }