diff --git a/mysql-test/main/long_unique_bugs.result b/mysql-test/main/long_unique_bugs.result
index 6bf3a7dcc44..3f65fb18014 100644
--- a/mysql-test/main/long_unique_bugs.result
+++ b/mysql-test/main/long_unique_bugs.result
@@ -809,3 +809,29 @@ hex(c1)	hex(c2)	c3	hex(c4)
 NULL	NULL	NULL	NULL
 drop table t1;
 # End of 10.5 tests
+#
+# MDEV-36852 Table definition gets corrupt after adding unique hash key
+#
+create table t1 (a text, b int, foreign key(a) references x(x)) engine=myisam;
+Warnings:
+Note	1071	Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` text DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  KEY `a` (`a`(1000))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+alter table t1 add unique(a), add key(a);
+Warnings:
+Note	1071	Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` text DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  UNIQUE KEY `a` (`a`) USING HASH,
+  KEY `a_2` (`a`(1000))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table t1;
+# End of 10.6 tests
diff --git a/mysql-test/main/long_unique_bugs.test b/mysql-test/main/long_unique_bugs.test
index b1daf97d194..d8d3462c1da 100644
--- a/mysql-test/main/long_unique_bugs.test
+++ b/mysql-test/main/long_unique_bugs.test
@@ -772,3 +772,15 @@ select hex(c1), hex(c2), c3, hex(c4) from t1;
 drop table t1;
 
 --echo # End of 10.5 tests
+
+--echo #
+--echo # MDEV-36852 Table definition gets corrupt after adding unique hash key
+--echo #
+
+create table t1 (a text, b int, foreign key(a) references x(x)) engine=myisam;
+show create table t1;
+alter table t1 add unique(a), add key(a);
+show create table t1;
+drop table t1;
+
+--echo # End of 10.6 tests
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 3a963403d65..69ddea8e5e9 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -3337,8 +3337,6 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
     Create_field *auto_increment_key= 0;
     Key_part_spec *column;
 
-    bool is_hash_field_needed= key->key_create_info.algorithm
-                               == HA_KEY_ALG_LONG_HASH;
     if (key->type == Key::IGNORE_KEY)
     {
       /* ignore redundant keys */
@@ -3349,6 +3347,9 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
 	break;
     }
 
+    bool is_hash_field_needed= key->key_create_info.algorithm
+                               == HA_KEY_ALG_LONG_HASH;
+
     if (key_check_without_overlaps(thd, create_info, alter_info, *key))
       DBUG_RETURN(true);
 
diff --git a/sql/table.cc b/sql/table.cc
index 9bbc29d4ecf..119d949388a 100644
--- a/sql/table.cc
+++ b/sql/table.cc
@@ -2838,6 +2838,7 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
         hash_keypart->fieldnr= hash_field_used_no + 1;
         hash_field= share->field[hash_field_used_no];
         hash_field->flags|= LONG_UNIQUE_HASH_FIELD;//Used in parse_vcol_defs
+        DBUG_ASSERT(hash_field->invisible == INVISIBLE_FULL);
         keyinfo->flags|= HA_NOSAME;
         share->virtual_fields++;
         share->stored_fields--;