diff --git a/asv_bench/benchmarks/index_object.py b/asv_bench/benchmarks/index_object.py
index f76040921393f..bbe164d4858ab 100644
--- a/asv_bench/benchmarks/index_object.py
+++ b/asv_bench/benchmarks/index_object.py
@@ -138,7 +138,8 @@ def setup(self, dtype):
         self.sorted = self.idx.sort_values()
         half = N // 2
         self.non_unique = self.idx[:half].append(self.idx[:half])
-        self.non_unique_sorted = self.sorted[:half].append(self.sorted[:half])
+        self.non_unique_sorted = (self.sorted[:half].append(self.sorted[:half])
+                                  .sort_values())
         self.key = self.sorted[N // 4]
 
     def time_boolean_array(self, dtype):