diff --git a/builders/windows-builder.py b/builders/windows-builder.py
index 7fac2fa..064749d 100644
--- a/builders/windows-builder.py
+++ b/builders/windows-builder.py
@@ -268,7 +268,7 @@ class WindowsBuilder(Builder):
         """
         Add extra arguments to the command line argument parser
         """
-        parser.add_argument('--portable', metavar='PATH', default=None,
+        parser.add_argument('--portable', metavar='PATH', action='store_true', default=False,
                             help='Specify the path to build the portable installation.')
 
     def setup_system_paths(self):
@@ -289,8 +289,6 @@ class WindowsBuilder(Builder):
         self.helpfile_path = os.path.join(self.manual_build_path, 'htmlhelp')
         self.winres_path = os.path.join(self.branch_path, 'resources', 'windows')
         self.pptviewlib_path = os.path.join(self.source_path, 'plugins', 'presentations', 'lib', 'pptviewlib')
-        if self.args.portable:
-            self.portable_dest_path = os.path.abspath(self.args.portable)
 
     def copy_extra_files(self):
         """
@@ -334,7 +332,7 @@ class WindowsBuilder(Builder):
         self._build_pptviewlib()
         self._create_innosetup_file()
         self._run_innosetup()
-        if self.portable_dest_path and os.path.exists(self.portable_dest_path):
+        if self.args.portable and os.path.exists(self.portable_dest_path):
             self._run_portableapp_builder()