diff --git a/scciclient/irmc/scci.py b/scciclient/irmc/scci.py
index 6dc6d30..9965c83 100755
--- a/scciclient/irmc/scci.py
+++ b/scciclient/irmc/scci.py
@@ -301,6 +301,16 @@ def scci_cmd(host, userid, password, cmd, port=443, auth_method='basic',
 
         if not do_async:
             time.sleep(5)
+        else:
+            # Async mode
+            # Even in async mode, return immediately may cause error 5
+            # (Input/Output error) for some commands such as POWER_ON,
+            # POWER_OFF, POWER_RESET if we perform multiple calls of them
+            # in a tight sequence or in parallel.
+            # So, we sleep some time for such commands.
+            if cmd in (POWER_ON, POWER_OFF, POWER_RESET):
+                time.sleep(3)
+
         if DEBUG:
             print(cmd)
             print(r.text)
diff --git a/scciclient/tests/irmc/test_scci.py b/scciclient/tests/irmc/test_scci.py
index 2573e15..300045a 100644
--- a/scciclient/tests/irmc/test_scci.py
+++ b/scciclient/tests/irmc/test_scci.py
@@ -270,7 +270,8 @@ class SCCITestCase(testtools.TestCase):
             'HTTP PROTOCOL ERROR, STATUS CODE = 302',
             str(e))
 
-    def test_power_on_ok(self):
+    @mock.patch.object(time, 'sleep')
+    def test_power_on_ok(self, mock_sleep):
         self.requests_mock.post("http://" + self.irmc_address + "/config",
                                 text="""<?xml version="1.0" encoding="UTF-8"?>
                                 <Status>
@@ -287,8 +288,10 @@ class SCCITestCase(testtools.TestCase):
                                  client_timeout=self.irmc_client_timeout)
         r = client(scci.POWER_ON)
         self.assertEqual(r.status_code, 200)
+        mock_sleep.assert_called_once_with(3)
 
-    def test_power_off_ok(self):
+    @mock.patch.object(time, 'sleep')
+    def test_power_off_ok(self, mock_sleep):
         self.requests_mock.post("http://" + self.irmc_address + "/config",
                                 text="""<?xml version="1.0" encoding="UTF-8"?>
                                 <Status>
@@ -305,6 +308,7 @@ class SCCITestCase(testtools.TestCase):
                                  client_timeout=self.irmc_client_timeout)
         r = client(scci.POWER_OFF)
         self.assertEqual(r.status_code, 200)
+        mock_sleep.assert_called_once_with(3)
 
     def test_power_cycle_ok(self):
         self.requests_mock.post("http://" + self.irmc_address + "/config",
@@ -324,7 +328,8 @@ class SCCITestCase(testtools.TestCase):
         r = client(scci.POWER_CYCLE)
         self.assertEqual(r.status_code, 200)
 
-    def test_power_reset_ok(self):
+    @mock.patch.object(time, 'sleep')
+    def test_power_reset_ok(self, mock_sleep):
         self.requests_mock.post("http://" + self.irmc_address + "/config",
                                 text="""<?xml version="1.0" encoding="UTF-8"?>
                                 <Status>
@@ -341,6 +346,7 @@ class SCCITestCase(testtools.TestCase):
                                  client_timeout=self.irmc_client_timeout)
         r = client(scci.POWER_RESET)
         self.assertEqual(r.status_code, 200)
+        mock_sleep.assert_called_once_with(3)
 
     def test_power_raise_nmi_ok(self):
         self.requests_mock.post("http://" + self.irmc_address + "/config",