diff --git a/test/shape/run-tests.py b/test/shape/run-tests.py
index 03f03df6c..471e7080c 100755
--- a/test/shape/run-tests.py
+++ b/test/shape/run-tests.py
@@ -20,10 +20,13 @@ if not args or args[0].find('hb-shape') == -1 or not os.path.exists (args[0]):
 	sys.exit ("""First argument does not seem to point to usable hb-shape.""")
 hb_shape, args = args[0], args[1:]
 
+env = os.environ.copy()
+env['LC_ALL'] = 'C'
 process = subprocess.Popen ([hb_shape, '--batch'],
 			    stdin=subprocess.PIPE,
 			    stdout=subprocess.PIPE,
-			    stderr=sys.stdout)
+			    stderr=sys.stdout,
+			    env=env)
 
 passes = 0
 fails = 0