diff --git a/hahomematic/support.py b/hahomematic/support.py
index f15c9f9a..6b47356e 100644
--- a/hahomematic/support.py
+++ b/hahomematic/support.py
@@ -247,8 +247,10 @@ def get_ip_addr(host: str, port: int) -> str | None:
     return local_ip
 
 
-def is_valid_hostname(hostname: str) -> bool:
+def is_valid_hostname(hostname: str | None) -> bool:
     """Return True if hostname is valid."""
+    if not hostname:
+        return False
     if hostname[-1] == ".":
         # strip exactly one dot from the right, if present
         hostname = hostname[:-1]
@@ -265,8 +267,10 @@ def is_valid_hostname(hostname: str) -> bool:
     return all(allowed.match(label) for label in labels)
 
 
-def is_valid_ipv4_address(address: str) -> bool:
+def is_valid_ipv4_address(address: str | None) -> bool:
     """Return True if ipv4_address is valid."""
+    if not address:
+        return False
     try:
         IPv4Address(address=address)
     except ValueError:
diff --git a/tests/test_support.py b/tests/test_support.py
index 5fe4d869..ba3e717b 100644
--- a/tests/test_support.py
+++ b/tests/test_support.py
@@ -550,6 +550,8 @@ def test_converter(
 
 def test_is_valid_hostname() -> None:
     """Test is_valid_hostname."""
+    assert is_valid_hostname(None) is False
+    assert is_valid_hostname("") is False
     assert is_valid_hostname(" ") is False
     assert is_valid_hostname("123") is False
     assert is_valid_hostname("ccu") is True
@@ -562,6 +564,7 @@ def test_is_valid_hostname() -> None:
 
 def test_is_valid_ipv4_address() -> None:
     """Test is_valid_ipv4_address."""
+    assert is_valid_ipv4_address(None) is False
     assert is_valid_ipv4_address("") is False
     assert is_valid_ipv4_address(" ") is False
     assert is_valid_ipv4_address("192.168.1782") is False