diff --git a/cowrie/commands/dd.py b/cowrie/commands/dd.py
index 3a11c317..47eeae8b 100644
--- a/cowrie/commands/dd.py
+++ b/cowrie/commands/dd.py
@@ -26,7 +26,7 @@ class command_dd(HoneyPotCommand):
             return
 
         for arg in self.args:
-            if not arg.index('='):
+            if arg.find('=') == -1:
                 self.write('unknown operand: {}'.format(arg))
                 HoneyPotCommand.exit(self)
             operand, value = arg.split('=')