--- a/testing/web-platform/mach_commands.py
+++ b/testing/web-platform/mach_commands.py
@@ -70,25 +70,33 @@ class WebPlatformTestsRunner(MozbuildObj
     def setup_kwargs_wptrun(self, kwargs):
         from wptrunner import wptcommandline
         here = os.path.join(self.topsrcdir, 'testing', 'web-platform')
 
         sys.path.insert(0, os.path.join(here, "tests", "tools"))
 
         import wptrun
 
+        product = kwargs["product"]
+
         setup_func = {
             "chrome": wptrun.setup_chrome,
             "edge": wptrun.setup_edge,
             "servo": wptrun.setup_servo,
-        }[kwargs["product"]]
+        }[product]
+
+        try:
+            wptrun.check_environ(product)
 
-        setup_func(wptrun.virtualenv.Virtualenv(self.virtualenv_manager.virtualenv_root),
-                   kwargs,
-                   True)
+            setup_func(wptrun.virtualenv.Virtualenv(self.virtualenv_manager.virtualenv_root),
+                       kwargs,
+                       True)
+        except wptrun.WptrunError as e:
+            print(e.message, file=sys.stderr)
+            sys.exit(1)
 
         kwargs["tests_root"] = os.path.join(here, "tests")
 
         if kwargs["metadata_root"] is None:
             metadir = os.path.join(here, "products", kwargs["product"])
             if not os.path.exists(metadir):
                 os.makedirs(metadir)
             kwargs["metadata_root"] = metadir