diff --git a/lib/sleep.py b/lib/sleep.py
index 4da57f4..d653872 100644
--- a/lib/sleep.py
+++ b/lib/sleep.py
@@ -9,8 +9,10 @@ def sleep_ms(duration):
     time.sleep_ms(duration)
 
 def sleep(duration):
-    # todo: deepsleep?
-    time.sleep(duration)
+    start_time = time.ticks_ms()
+    end_time = start_time + duration * 1000
+    while time.ticks_ms() < end_time:
+        wfi()
 
 def wfi():
     # todo: this is fake
diff --git a/lib/test_sleep.py b/lib/test_sleep.py
index 977b667..b653f92 100644
--- a/lib/test_sleep.py
+++ b/lib/test_sleep.py
@@ -3,12 +3,16 @@
 ___license___      = "MIT"
 ___dependencies___ = ["upip:unittest", "sleep"]
 
-import unittest, sleep
+import unittest, sleep, time
 
 class TestSleep(unittest.TestCase):
 
     def test_sleep(self):
-        sleep.sleep_ms(100)
+        sleep_secs = 5
+        time_before = time.ticks_ms()
+        time_after = time_before + 1000 * sleep_secs
+        sleep.sleep(sleep_secs)
+        self.assertTrue(time.ticks_ms() >= time_after)
 
 if __name__ == '__main__':
     unittest.main()