diff --git a/ring_mon/apply-state b/ring_mon/apply-state
index 096d29d..727e0e4 100755
--- a/ring_mon/apply-state
+++ b/ring_mon/apply-state
@@ -65,7 +65,10 @@ class LightManager:
         env = os.environ.copy()
         env["DEVICE_NUMBER"] = str(self.device_number)
 
-        Popen([str(self.args.bin_set_light.resolve()), "on" if on else "off"], env=env)
+        p = Popen(
+            [str(self.args.bin_set_light.resolve()), "on" if on else "off"], env=env
+        )
+        p.communicate()
 
     def do_waveform(self, status) -> tuple:
         last_set = None