diff --git a/src/Utils.php b/src/Utils.php
index 1a506d6..8c4d607 100644
--- a/src/Utils.php
+++ b/src/Utils.php
@@ -79,14 +79,20 @@ public static function base64url_decode($data) {
     ."'connectionKey' and 'clientId' as keys. 'clientId' is null if connection is not identified";
 
     /**
+     * @return object
      * @throws AblyException
      */
-    public static function decodeSocketId($socketId) {
+    public static function decodeSocketId($socketId): ?object
+    {
         $socketIdObject = null;
         if ($socketId) {
-            $socketIdObject = json_decode(self::base64url_decode($socketId));
-            if (!$socketIdObject) {
-                throw new AblyException("SocketId decoding failed, ".self::SOCKET_ID_ERROR);
+            $socketIdJsonString = self::base64url_decode($socketId);
+            if (!$socketIdJsonString) {
+                throw new AblyException("Base64 decoding failed, ".self::SOCKET_ID_ERROR);
+            }
+            $socketIdObject = json_decode($socketIdJsonString);
+            if (json_last_error() !== JSON_ERROR_NONE) {
+                throw new AblyException("JSON decoding failed: " . json_last_error_msg() . ", " . self::SOCKET_ID_ERROR);
             }
             if (!isset($socketIdObject->connectionKey)) {
                 throw new AblyException("ConnectionKey is not set, ".self::SOCKET_ID_ERROR);
diff --git a/tests/UtilsTest.php b/tests/UtilsTest.php
index 3fb3663..a4362fd 100644
--- a/tests/UtilsTest.php
+++ b/tests/UtilsTest.php
@@ -53,7 +53,7 @@ public function testDecodeSocketId() {
     public function testExceptionOnDecodingInvalidSocketId()
     {
         self::expectException(AblyException::class);
-        self::expectExceptionMessage("SocketId decoding failed, ".Utils::SOCKET_ID_ERROR);
+        self::expectExceptionMessage("Base64 decoding failed, ".Utils::SOCKET_ID_ERROR);
         Utils::decodeSocketId("invalid_socket_id");
     }