diff --git a/pyfritzhome/fritzhome.py b/pyfritzhome/fritzhome.py
index 38916ca..1ca8442 100644
--- a/pyfritzhome/fritzhome.py
+++ b/pyfritzhome/fritzhome.py
@@ -37,6 +37,7 @@ def __init__(self, host, user, password, ssl_verify=True):
         self._session = Session()
         self._ssl_verify = ssl_verify
         self._has_getdeviceinfos = True
+        self._has_txbusy = True
 
     def _request(self, url, params=None, timeout=10):
         """Send a request with parameters."""
@@ -200,9 +201,13 @@ def _get_listinfo_elements(self, entity_type):
 
     def wait_device_txbusy(self, ain, retries=10):
         """Wait for device to finish command execution."""
+        if not self._has_txbusy:
+            return True
+
         for _ in range(retries):
             if self._has_getdeviceinfos:
                 try:
+                    # getdeviceinfos was added in FritzOS 7.24
                     plain = self.get_device_infos(ain)
                     dom = ElementTree.fromstring(plain)
                 except exceptions.HTTPError:
@@ -213,8 +218,14 @@ def wait_device_txbusy(self, ain, retries=10):
                 dom = self.get_device_element(ain)
 
             txbusy = dom.findall("txbusy")
+            if not txbusy:
+                # txbusy was added in FritzOS 7.20
+                self._has_txbusy = False
+                return True
+
             if txbusy[0].text == "0":
                 return True
+
             time.sleep(0.2)
         return False
 
diff --git a/tests/responses/base/device_list_no_txbusy.xml b/tests/responses/base/device_list_no_txbusy.xml
new file mode 100644
index 0000000..36d43fb
--- /dev/null
+++ b/tests/responses/base/device_list_no_txbusy.xml
@@ -0,0 +1,25 @@
+<?xml version="1.0" ?>
+<devicelist version="1">
+    <device functionbitmask="320" fwversion="03.54" id="18" identifier="32960 0089208" manufacturer="AVM" productname="Comet DECT">
+        <present>0</present>
+        <name>Kitchen</name>
+        <temperature>
+            <celsius/>
+            <offset/>
+        </temperature>
+        <hkr>
+            <tist/>
+            <tsoll/>
+            <absenk/>
+            <komfort/>
+            <lock/>
+            <devicelock/>
+            <errorcode>0</errorcode>
+            <batterylow>0</batterylow>
+            <nextchange>
+                <endperiod>0</endperiod>
+                <tchange>255</tchange>
+            </nextchange>
+        </hkr>
+    </device>
+</devicelist>
\ No newline at end of file
diff --git a/tests/test_fritzhome.py b/tests/test_fritzhome.py
index b7e56f5..9a11167 100644
--- a/tests/test_fritzhome.py
+++ b/tests/test_fritzhome.py
@@ -345,15 +345,44 @@ def test_wait_tx_busy(self):
         ]
 
         assert self.fritz.wait_device_txbusy("11960 0089208")
+        assert self.mock.call_count == 2
 
     def test_wait_tx_busy_fallback(self):
+        """FritzOS <7.24 has no getdeviceinfos"""
         self.mock.side_effect = [
             HTTPError("400 Client Error: Bad Request"),
             Helper.response("base/device_list_txbusy"),
             Helper.response("base/device_list_not_txbusy"),
         ]
 
+        # first call will set _has_getdeviceinfos to False
+        # so sub-sequent calls won't try getdeviceinfos anymore
         assert self.fritz.wait_device_txbusy("22960 0089208")
+        assert self.mock.call_count == 3
+
+        self.mock.reset_mock()
+        self.mock.side_effect = [
+            Helper.response("base/device_list_txbusy"),
+            Helper.response("base/device_list_not_txbusy"),
+        ]
+
+        assert self.fritz.wait_device_txbusy("22960 0089208")
+        assert self.mock.call_count == 2
+
+    def test_wait_tx_busy_no_txbusy(self):
+        """FritzOS <7.20 has no txbusy and no getdeviceinfos"""
+        self.mock.side_effect = [
+            HTTPError("400 Client Error: Bad Request"),
+            Helper.response("base/device_list_no_txbusy"),
+        ]
+
+        # first call will set _has_txbusy to False, those skip all sub-sequent calls
+        assert self.fritz.wait_device_txbusy("32960 0089208")
+        assert self.mock.call_count == 2
+        self.mock.reset_mock()
+
+        assert self.fritz.wait_device_txbusy("32960 0089208")
+        assert self.mock.call_count == 0
 
     def test_wait_tx_busy_failed(self):
         self.mock.side_effect = [
@@ -362,3 +391,4 @@ def test_wait_tx_busy_failed(self):
         ]
 
         assert not self.fritz.wait_device_txbusy("11960 0089208", 1)
+        assert self.mock.call_count == 1