--- a/src/engine/SCons/Script/Main.py
+++ b/src/engine/SCons/Script/Main.py
@@ -1253,7 +1253,11 @@ def _build_targets(fs, options, targets,
     BuildTask.options = options
 
 
-    python_has_threads = sysconfig.get_config_var('WITH_THREAD')
+    # As of 3.7, python removed support for threadless platforms.
+    # See https://www.python.org/dev/peps/pep-0011/
+    is_37_or_later = sys.version_info.major > 3 or \
+        sys.version_info.major == 3 and sys.version_info.minor >= 7
+    python_has_threads = sysconfig.get_config_var('WITH_THREAD') or is_37_or_later
     # to check if python configured with threads.
     global num_jobs
     num_jobs = options.num_jobs
--- a/runtest.py
+++ b/runtest.py
@@ -781,7 +781,7 @@ tests_passing = 0
 tests_failing = 0
 
 
-def run_test(t, io_lock, async=True):
+def run_test(t, io_lock, run_async=True):
     global tests_completed, tests_passing, tests_failing
     header = ""
     command_args = ['-tt']