diff --git a/src/PhoneNumberLookup/Models/OrderRequest.php b/src/PhoneNumberLookup/Models/OrderRequest.php
index f400a76..e8e077f 100644
--- a/src/PhoneNumberLookup/Models/OrderRequest.php
+++ b/src/PhoneNumberLookup/Models/OrderRequest.php
@@ -31,7 +31,7 @@ public function __construct()
     /**
      * Encode this object to JSON
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         $json = array();
         $json['tns'] = isset($this->tns) ?
diff --git a/src/PhoneNumberLookup/Models/OrderResponse.php b/src/PhoneNumberLookup/Models/OrderResponse.php
index ba2346c..1129b98 100644
--- a/src/PhoneNumberLookup/Models/OrderResponse.php
+++ b/src/PhoneNumberLookup/Models/OrderResponse.php
@@ -39,7 +39,7 @@ public function __construct()
     /**
      * Encode this object to JSON
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         $json = array();
         $json['requestId'] = $this->requestId;
diff --git a/src/PhoneNumberLookup/Models/OrderStatus.php b/src/PhoneNumberLookup/Models/OrderStatus.php
index bd93e24..a3d3d99 100644
--- a/src/PhoneNumberLookup/Models/OrderStatus.php
+++ b/src/PhoneNumberLookup/Models/OrderStatus.php
@@ -55,7 +55,7 @@ public function __construct()
     /**
      * Encode this object to JSON
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         $json = array();
         $json['requestId']              = $this->requestId;
diff --git a/src/PhoneNumberLookup/Models/Result.php b/src/PhoneNumberLookup/Models/Result.php
index a278d99..2547eff 100644
--- a/src/PhoneNumberLookup/Models/Result.php
+++ b/src/PhoneNumberLookup/Models/Result.php
@@ -96,7 +96,7 @@ public function __construct()
     /**
      * Encode this object to JSON
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         $json = array();
         $json['Response Code']       = $this->responseCode;