diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index eeeb8d1..f6eb659 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -923,7 +923,7 @@
                                  fatal=False)
 
         # Find any extranious keys for this project and remove them
-        for key in list(self.options.keys() - options.keys()):
+        for key in self.options.keys() - options.keys():
             if key.is_project() and key.subproject == subproject:
                 del self.options[key]