diff --git a/src/_pytest/mark/legacy.py b/src/_pytest/mark/legacy.py
index 651288cb8..766b8f9bd 100644
--- a/src/_pytest/mark/legacy.py
+++ b/src/_pytest/mark/legacy.py
@@ -63,7 +63,7 @@ class KeywordMapping:
 
         """
         subname = subname.lower()
-        names = [name.lower() for name in self._names]
+        names = (name.lower() for name in self._names)
 
         for name in names:
             if subname in name: