diff --git a/mysql-test/suite/innodb/r/alter_table.result b/mysql-test/suite/innodb/r/alter_table.result
index 2fb09e2fe5c..e47bfb90152 100644
--- a/mysql-test/suite/innodb/r/alter_table.result
+++ b/mysql-test/suite/innodb/r/alter_table.result
@@ -38,3 +38,18 @@ Warnings:
 Warning	1105	ORDER BY ignored as there is a user-defined clustered index in the table 't1'
 DROP TABLE t1;
 SET sql_mode=DEFAULT;
+#
+# MDEV-18775 Server crashes in dict_table_t::instant_column
+# upon ADD COLUMN
+#
+CREATE TABLE tx (pk INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t1 (pk INT, a INT, PRIMARY KEY (pk), KEY (a), FOREIGN KEY (a) REFERENCES tx (pk)) ENGINE=InnoDB;
+SET FOREIGN_KEY_CHECKS=OFF;
+ALTER TABLE t1 DROP a;
+ERROR HY000: Cannot drop column 'a': needed in a foreign key constraint 'test/t1_ibfk_1'
+SET FOREIGN_KEY_CHECKS=ON;
+ALTER TABLE t1 ADD b INT;
+ALTER TABLE t1 DROP a;
+ERROR HY000: Cannot drop index 'a': needed in a foreign key constraint
+ALTER TABLE t1 ADD c INT;
+DROP TABLE t1, tx;
diff --git a/mysql-test/suite/innodb/t/alter_table.test b/mysql-test/suite/innodb/t/alter_table.test
index ece24eb45c7..d0943e7d407 100644
--- a/mysql-test/suite/innodb/t/alter_table.test
+++ b/mysql-test/suite/innodb/t/alter_table.test
@@ -38,3 +38,24 @@ ALTER TABLE t1 ORDER BY a;
 DROP TABLE t1;
 
 SET sql_mode=DEFAULT;
+
+--echo #
+--echo # MDEV-18775 Server crashes in dict_table_t::instant_column
+--echo # upon ADD COLUMN
+--echo #
+
+CREATE TABLE tx (pk INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t1 (pk INT, a INT, PRIMARY KEY (pk), KEY (a), FOREIGN KEY (a) REFERENCES tx (pk)) ENGINE=InnoDB;
+
+SET FOREIGN_KEY_CHECKS=OFF;
+
+--error ER_FK_COLUMN_CANNOT_DROP
+ALTER TABLE t1 DROP a;
+
+SET FOREIGN_KEY_CHECKS=ON;
+
+ALTER TABLE t1 ADD b INT;
+--error ER_DROP_INDEX_FK
+ALTER TABLE t1 DROP a;
+ALTER TABLE t1 ADD c INT;
+DROP TABLE t1, tx;
diff --git a/storage/innobase/handler/handler0alter.cc b/storage/innobase/handler/handler0alter.cc
index 47cc31ce9dc..c04c69ba8e2 100644
--- a/storage/innobase/handler/handler0alter.cc
+++ b/storage/innobase/handler/handler0alter.cc
@@ -5142,14 +5142,12 @@ error_handled:
 	ut_ad(!user_table->drop_aborted);
 
 err_exit:
-#ifdef UNIV_DEBUG
 	/* Clear the to_be_dropped flag in the data dictionary cache. */
 	for (ulint i = 0; i < ctx->num_to_drop_index; i++) {
 		DBUG_ASSERT(ctx->drop_index[i]->is_committed());
 		DBUG_ASSERT(ctx->drop_index[i]->to_be_dropped);
 		ctx->drop_index[i]->to_be_dropped = 0;
 	}
-#endif /* UNIV_DEBUG */
 
 	row_mysql_unlock_data_dictionary(ctx->trx);