diff --git a/mysql-test/r/bug115840.result b/mysql-test/r/bug115840.result
new file mode 100644
index 00000000000..30c77f74ce7
--- /dev/null
+++ b/mysql-test/r/bug115840.result
@@ -0,0 +1,48 @@
+#
+# Bug#115840: Incorrect Cost Display for Join with Materialized Subquery
+#
+SET @old_optimizer_switch= @@optimizer_switch;
+SET optimizer_switch="firstmatch=off,duplicateweedout=off";
+drop table if exists t1;
+CREATE TABLE t1 ( a INTEGER NOT NULL, b INTEGER NOT NULL );
+INSERT INTO t1 VALUES (1,1), (2,2), (3,3);
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+EXPLAIN FORMAT=tree SELECT a FROM t1 WHERE a NOT IN ( SELECT b FROM t1 WHERE b > 2 );
+EXPLAIN
+-> Nested loop antijoin  (rows=3)
+    -> Table scan on t1  (rows=3)
+    -> Single-row index lookup on <subquery2> using <auto_distinct_key> (b=t1.a)  (rows=1)
+        -> Materialize with deduplication  (rows=3)
+            -> Filter: (t1.b is not null)  (rows=3)
+                -> Filter: (t1.b > 2)  (rows=3)
+                    -> Table scan on t1  (rows=3)
+
+DROP TABLE t1;
+CREATE TABLE t1 ( f1 TIME, f2 VARCHAR(1) );
+INSERT INTO t1 VALUES ('08:35:24', 'X'), ('14:51:13', 'S'), ('11:22:33', 'Q');
+drop table if exists t2;
+CREATE TABLE t2 ( pk INTEGER );
+INSERT INTO t2 VALUES (1), (2);
+ANALYZE TABLE t1, t2;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+test.t2	analyze	status	OK
+EXPLAIN FORMAT=tree SELECT * FROM t1 WHERE EXISTS ( SELECT alias1.f2 FROM t2 LEFT JOIN t1 ON 1 LEFT JOIN t1 AS alias1 ON 1 );
+EXPLAIN
+-> Inner hash join (no condition)  (rows=3)
+    -> Table scan on t1  (rows=3)
+    -> Hash
+        -> Constant row from <subquery2>  (rows=1)
+            -> Materialize with deduplication  (rows=18)
+                -> Left hash join (no condition)  (rows=18)
+                    -> Left hash join (no condition)  (rows=6)
+                        -> Table scan on t2  (rows=2)
+                        -> Hash
+                            -> Table scan on t1  (rows=3)
+                    -> Hash
+                        -> Table scan on alias1  (rows=3)
+
+DROP TABLE t1, t2;
+SET optimizer_switch= @old_optimizer_switch;
diff --git a/mysql-test/t/bug115840.test b/mysql-test/t/bug115840.test
new file mode 100644
index 00000000000..e9f2f97fdeb
--- /dev/null
+++ b/mysql-test/t/bug115840.test
@@ -0,0 +1,33 @@
+--echo #
+--echo # Bug#115840: Incorrect Cost Display for Join with Materialized Subquery
+--echo #
+--source include/elide_costs.inc
+
+SET @old_optimizer_switch= @@optimizer_switch;
+
+SET optimizer_switch="firstmatch=off,duplicateweedout=off";
+--disable_warnings
+drop table if exists t1;
+CREATE TABLE t1 ( a INTEGER NOT NULL, b INTEGER NOT NULL );
+INSERT INTO t1 VALUES (1,1), (2,2), (3,3);
+--enable_warnings
+ANALYZE TABLE t1;
+
+--replace_regex $elide_costs
+EXPLAIN FORMAT=tree SELECT a FROM t1 WHERE a NOT IN ( SELECT b FROM t1 WHERE b > 2 );
+DROP TABLE t1;
+
+CREATE TABLE t1 ( f1 TIME, f2 VARCHAR(1) );
+INSERT INTO t1 VALUES ('08:35:24', 'X'), ('14:51:13', 'S'), ('11:22:33', 'Q');
+--disable_warnings
+drop table if exists t2;
+CREATE TABLE t2 ( pk INTEGER );
+INSERT INTO t2 VALUES (1), (2);
+ANALYZE TABLE t1, t2;
+--enable_warnings
+
+--replace_regex $elide_costs
+EXPLAIN FORMAT=tree SELECT * FROM t1 WHERE EXISTS ( SELECT alias1.f2 FROM t2 LEFT JOIN t1 ON 1 LEFT JOIN t1 AS alias1 ON 1 );
+
+DROP TABLE t1, t2;
+SET optimizer_switch= @old_optimizer_switch;
diff --git a/sql/sql_executor.cc b/sql/sql_executor.cc
index 50010a2d111..34f82794da9 100644
--- a/sql/sql_executor.cc
+++ b/sql/sql_executor.cc
@@ -1895,14 +1895,23 @@ void SetCostOnNestedLoopAccessPath(const Cost_model_server &cost_model,
     return;
   }
 
+  // If the type of the table is MATERIALIZE, we should use its table_path
+  // to estimate the number of rows after the join. (Bug#115840)
+  auto inner_output_rows = (inner->type == AccessPath::MATERIALIZE)
+                               ? inner->materialize().table_path->num_output_rows()
+                               : inner->num_output_rows();
+  auto outer_output_rows = (outer->type == AccessPath::MATERIALIZE)
+                               ? outer->materialize().table_path->num_output_rows()
+                               : outer->num_output_rows();
+
   // Mirrors set_prefix_join_cost(), even though the cost calculation doesn't
   // make a lot of sense.
   double inner_expected_rows_before_filter =
       pos_inner->filter_effect > 0.0
-          ? (inner->num_output_rows() / pos_inner->filter_effect)
+          ? (inner_output_rows / pos_inner->filter_effect)
           : 0.0;
   double joined_rows =
-      outer->num_output_rows() * inner_expected_rows_before_filter;
+      outer_output_rows * inner_expected_rows_before_filter;
   path->set_num_output_rows(joined_rows * pos_inner->filter_effect);
   path->cost = outer->cost + pos_inner->read_cost +
                cost_model.row_evaluate_cost(joined_rows);
@@ -1923,9 +1932,17 @@ void SetCostOnHashJoinAccessPath(const Cost_model_server &cost_model,
     return;
   }
 
+  // Mirrors SetCostOnNestedLoopAccessPath().
+  auto inner_output_rows = (inner->type == AccessPath::MATERIALIZE)
+                               ? inner->materialize().table_path->num_output_rows()
+                               : inner->num_output_rows();
+  auto outer_output_rows = (outer->type == AccessPath::MATERIALIZE)
+                               ? outer->materialize().table_path->num_output_rows()
+                               : outer->num_output_rows();
+
   // Mirrors set_prefix_join_cost(), even though the cost calculation doesn't
   // make a lot of sense.
-  double joined_rows = outer->num_output_rows() * inner->num_output_rows();
+  double joined_rows = outer_output_rows * inner_output_rows;
   path->set_num_output_rows(joined_rows * pos_outer->filter_effect);
   path->cost = inner->cost + pos_outer->read_cost +
                cost_model.row_evaluate_cost(joined_rows);