--- a/scripts/desktop_unittest.py
+++ b/scripts/desktop_unittest.py
@@ -255,17 +255,17 @@ class DesktopUnittest(TestingMixin, Merc
         return self.symbols_url
 
     def _query_abs_base_cmd(self, suite_category):
         if self.binary_path:
             c = self.config
             dirs = self.query_abs_dirs()
             run_file = c['run_file_names'][suite_category]
             base_cmd = [self.query_python_path('python'), '-u']
-            base_cmd.append(dirs["abs_%s_dir" % suite_category] + "/" + run_file)
+            base_cmd.append(os.path.join(dirs["abs_%s_dir" % suite_category], run_file))
             abs_app_dir = self.query_abs_app_dir()
 
             webapprt_path = os.path.join(os.path.dirname(self.binary_path),
                                          'webapprt-stub')
             if c.get('exe_suffix'):
                 webapprt_path += c['exe_suffix']
 
             str_format_values = {