diff --git a/src/calibre/utils/formatter_functions.py b/src/calibre/utils/formatter_functions.py
index 8f2833050f..cbcf33f32f 100644
--- a/src/calibre/utils/formatter_functions.py
+++ b/src/calibre/utils/formatter_functions.py
@@ -717,15 +717,23 @@ class BuiltinSubitems(BuiltinFormatterFunction):
             return ''
         si = int(start_index)
         ei = int(end_index)
+        has_periods = '.' in val
         items = [v.strip() for v in val.split(',')]
         rv = set()
+        if has_periods:
+            pp = re.compile(r'(?<=[^\.\s])\.(?=[^\.\s])', re.U)
+        else:
+            pp = None
         for item in items:
-            component = item.split('.')
+            if has_periods and '.' in item:
+                components = pp.split(item)
+            else:
+                components = [item]
             try:
                 if ei == 0:
-                    rv.add('.'.join(component[si:]))
+                    rv.add('.'.join(components[si:]))
                 else:
-                    rv.add('.'.join(component[si:ei]))
+                    rv.add('.'.join(components[si:ei]))
             except:
                 pass
         return ', '.join(sorted(rv, key=sort_key))