diff --git a/docs/en/sonar.md b/docs/en/sonar.md
index bc515dfd..1ec802d5 100644
--- a/docs/en/sonar.md
+++ b/docs/en/sonar.md
@@ -70,6 +70,7 @@ def fall(gpio, level, tick):
     done.set()
 
 def read_distance():
+    global low
     done.clear()
     pi.gpio_trigger(TRIG, 50, 1)
     done.wait(timeout=5)
diff --git a/docs/ru/sonar.md b/docs/ru/sonar.md
index 8d92ddce..be979100 100644
--- a/docs/ru/sonar.md
+++ b/docs/ru/sonar.md
@@ -70,6 +70,7 @@ def fall(gpio, level, tick):
     done.set()
 
 def read_distance():
+    global low
     done.clear()
     pi.gpio_trigger(TRIG, 50, 1)
     done.wait(timeout=5)