diff -Naur a/Nagstamon/Helpers.py b/Nagstamon/Helpers.py
--- a/Nagstamon/Helpers.py	2020-08-26 13:59:13.582204042 +0200
+++ b/Nagstamon/Helpers.py	2020-08-26 14:08:35.036908166 +0200
@@ -454,14 +454,18 @@
             for property in os_release_file.read_text().splitlines():
                 key, value = property.split('=', 1)
                 os_release_dict[key] = value.strip('"').strip("'")
-            return (os_release_dict['ID'], os_release_dict['VERSION_ID'], os_release_dict['NAME'])
+            return (os_release_dict.get('ID').lower(),
+                    os_release_dict.get('VERSION_ID', 'unknown').lower(),
+                    os_release_dict.get('NAME').lower())
         else:
             return False
     else:
-        return platform.dist()
+        # fix for non-working build on Debian<10
+        dist_name, dist_version, dist_id = platform.dist()
+        return dist_name.lower(), dist_version, dist_id
 
 
-    # depending on column different functions have to be used
+# depending on column different functions have to be used
 # 0 + 1 are column "Hosts", 1 + 2 are column "Service" due to extra font flag pictograms
 SORT_COLUMNS_FUNCTIONS = {0: compare_host,
         1: compare_host,