diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index e319118c..f0e5a9ea 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -2084,6 +2084,11 @@ class Net_SSH2 {
         if ($response === false) {
             return false;
         }
+        
+        if (ord($response[0]) != NET_SSH2_MSG_CHANNEL_SUCCESS) {
+            user_error('exec call refused');
+            return;
+        }
 
         $this->channel_status[NET_SSH2_CHANNEL_EXEC] = NET_SSH2_MSG_CHANNEL_DATA;