--- a/testing/talos/talos/ttest.py
+++ b/testing/talos/talos/ttest.py
@@ -89,21 +89,21 @@ class TTest(object):
         # in test.py configs
         here = os.path.dirname(os.path.realpath(__file__))
         if test_config['mainthread']:
             mainthread_io = os.path.join(here, "mainthread_io.log")
             setup.env['MOZ_MAIN_THREAD_IO_LOG'] = mainthread_io
 
         # As we transition to Stylo, we need to set env vars and output data properly
         if browser_config['stylo']:
-            setup.env['STYLO_FORCE_ENABLED'] = 1
+            setup.env['STYLO_FORCE_ENABLED'] = '1'
 
         # During the Stylo transition, measure different number of threads
         if browser_config.get('stylothreads', 0) > 0:
-            setup.env['STYLO_THREADS'] = browser_config['stylothreads']
+            setup.env['STYLO_THREADS'] = str(browser_config['stylothreads'])
 
         test_config['url'] = utils.interpolate(
             test_config['url'],
             profile=setup.profile_dir,
             firefox=browser_config['browser_path']
         )
 
         # setup global (cross-cycle) counters: