diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 7fa0ea1..420cb9b 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -39,6 +39,8 @@ jobs:
           - "8.0"
           - "8.1"
           - "8.2"
+          - "8.3"
+          - "8.4"
 
     steps:
       - name: Checkout.
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index 3e79b31..0d90f64 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -35,6 +35,7 @@ jobs:
           - "8.0"
           - "8.1"
           - "8.2"
+          - "8.3"
 
     steps:
       - name: Checkout.
diff --git a/src/SapiEmitter.php b/src/SapiEmitter.php
index feab6cb..7048042 100644
--- a/src/SapiEmitter.php
+++ b/src/SapiEmitter.php
@@ -32,7 +32,7 @@ final class SapiEmitter implements EmitterInterface
      * @param int|null $bufferLength
      * @throws InvalidArgumentException if buffer length is integer type and less than or one.
      */
-    public function __construct(int $bufferLength = null)
+    public function __construct(?int $bufferLength = null)
     {
         if ($bufferLength !== null && $bufferLength < 1) {
             throw new InvalidArgumentException(sprintf(