diff --git a/src/server/util/interface_util.py b/src/server/util/interface_util.py
index 5a02525..b2ef60a 100644
--- a/src/server/util/interface_util.py
+++ b/src/server/util/interface_util.py
@@ -79,6 +79,8 @@ def is_managed_by_network_manager(cls, interface):
         for line in conf_data:
             if line.startswith("unmanaged-devices=") and "mac:" + cls.get_mac(interface) not in line:
                 managed = True  # Ensure configs with duplicates raise an unmanaged prompt
+        if "unmanaged-devices=" not in " ".join(conf_data):
+            managed = True
         Logger.debug("Interface \"%s\" managed by network manager: %s", interface, managed)
         return managed