diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index 3b55d7a0..ac499c96 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -2532,7 +2532,7 @@ class SSH2
      * @psalm-return ($callback is callable ? bool : string|bool)
      * @throws \RuntimeException on connection error
      */
-    public function exec(string $command, callable $callback = null)
+    public function exec(string $command, $callback = null)
     {
         $this->curTimeout = $this->timeout;
         $this->is_timeout = false;
@@ -2623,7 +2623,7 @@ class SSH2
 
         $this->channel_status[self::CHANNEL_EXEC] = MessageType::CHANNEL_DATA;
 
-        if ($callback === null || $this->in_request_pty_exec) {
+        if ($callback === false || $this->in_request_pty_exec) {
             return true;
         }