"Return a hash-table containing only the entries in Table1 whose key is not
also a key in Table2." (declare (type hash-table table1 table2))
(let ((res (make-hash-table-like table1)))
- (with-locked-hash-table (table2)
+ (with-locked-system-table (table2)
(dohash ((k v) table1 :locked t)
(unless (nth-value 1 (gethash k table2))
(setf (gethash k res) v))))