diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 35014674565ff..d77f973f124b1 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -8024,7 +8024,7 @@ def asof(self, where, subset=None):
                     np.nan, index=self.columns, name=where[0]
                 )
 
-        locs = self.index.asof_locs(where, ~(nulls._values))
+        locs = self.index.asof_locs(where, ~cast("DataFrame", nulls._values))
 
         # mask the missing
         mask = locs == -1