diff --git a/python_terraform/__init__.py b/python_terraform/__init__.py
index fd2ce5b..9abb999 100644
--- a/python_terraform/__init__.py
+++ b/python_terraform/__init__.py
@@ -39,7 +39,7 @@ class Terraform:
     def _gen_param_string(self, kargs):
         params = []
         for key, value in kargs.items():
-            if not value:
+            if value:
                 params += ['-%s=%s' % (key, value)]
             else:
                 params += ['-%s' % key]