diff --git a/mysql-test/main/trigger_null.result b/mysql-test/main/trigger_null.result
index 4e4a99f22a3..42122e59e2c 100644
--- a/mysql-test/main/trigger_null.result
+++ b/mysql-test/main/trigger_null.result
@@ -399,4 +399,19 @@ Warnings:
 Warning	1364	Field 'c5' doesn't have a default value
 drop table t1;
 set sql_mode=default;
+#
+# MDEV-36026 Problem with INSERT SELECT on NOT NULL columns while having BEFORE UPDATE trigger
+#
+create table t1 (b int(11) not null);
+create trigger t1bu before update on t1 for each row begin end;
+insert t1 (b) select 1 union select 2;
+create trigger trgi before insert on t1 for each row set new.b=ifnull(new.b,10);
+insert t1 (b) select NULL union select 11;
+select * from t1;
+b
+1
+2
+10
+11
+drop table t1;
 # End of 10.5 tests
diff --git a/mysql-test/main/trigger_null.test b/mysql-test/main/trigger_null.test
index 3aa39ded586..935152e376a 100644
--- a/mysql-test/main/trigger_null.test
+++ b/mysql-test/main/trigger_null.test
@@ -425,4 +425,15 @@ insert into t1 (c) values (1);
 drop table t1;
 set sql_mode=default;
 
+--echo #
+--echo # MDEV-36026 Problem with INSERT SELECT on NOT NULL columns while having BEFORE UPDATE trigger
+--echo #
+create table t1 (b int(11) not null);
+create trigger t1bu before update on t1 for each row begin end;
+insert t1 (b) select 1 union select 2;
+create trigger trgi before insert on t1 for each row set new.b=ifnull(new.b,10);
+insert t1 (b) select NULL union select 11;
+select * from t1;
+drop table t1;
+
 --echo # End of 10.5 tests
diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc
index d19821a28e6..759d7750805 100644
--- a/sql/sql_insert.cc
+++ b/sql/sql_insert.cc
@@ -4248,6 +4248,7 @@ select_insert::prepare(List<Item> &values, SELECT_LEX_UNIT *u)
 int select_insert::prepare2(JOIN *)
 {
   DBUG_ENTER("select_insert::prepare2");
+  switch_to_nullable_trigger_fields(*fields, table);
   if (table->validate_default_values_of_unset_fields(thd))
     DBUG_RETURN(1);
   if (thd->lex->describe)