diff --git a/mysql-test/main/long_unique_bugs.result b/mysql-test/main/long_unique_bugs.result
index c85f5d5b21e..1caec209d9f 100644
--- a/mysql-test/main/long_unique_bugs.result
+++ b/mysql-test/main/long_unique_bugs.result
@@ -729,4 +729,16 @@ alter table t1 enable keys;
 insert into t1 values (2);
 ERROR 23000: Duplicate entry '2' for key 'i'
 drop table t1;
+#
+# MDEV-25654 Unexpected ER_CRASHED_ON_USAGE and Assertion `limit >= trx_id' failed in purge_node_t::skip
+#
+create table t1 (a int, unique using hash (a)) engine=innodb
+partition by range(a) (
+partition p1 values less than (2),
+partition p2 values less than (101)
+);
+insert into t1 select seq from seq_1_to_100;
+alter table t1 add partition (partition p3 values less than (maxvalue));
+alter table t1 force;
+drop table t1;
 # End of 10.5 tests
diff --git a/mysql-test/main/long_unique_bugs.test b/mysql-test/main/long_unique_bugs.test
index 2f85328bda3..6ad59fe6495 100644
--- a/mysql-test/main/long_unique_bugs.test
+++ b/mysql-test/main/long_unique_bugs.test
@@ -706,4 +706,19 @@ alter table t1 enable keys;
 insert into t1 values (2);
 drop table t1;
 
+--echo #
+--echo # MDEV-25654 Unexpected ER_CRASHED_ON_USAGE and Assertion `limit >= trx_id' failed in purge_node_t::skip
+--echo #
+create table t1 (a int, unique using hash (a)) engine=innodb
+partition by range(a) (
+  partition p1 values less than (2),
+  partition p2 values less than (101)
+);
+insert into t1 select seq from seq_1_to_100;
+
+alter table t1 add partition (partition p3 values less than (maxvalue));
+alter table t1 force;
+
+drop table t1;
+
 --echo # End of 10.5 tests
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 64c142e6df3..e744ab78a2f 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -9264,7 +9264,20 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       LEX_CSTRING tmp_name;
       bzero((char*) &key_create_info, sizeof(key_create_info));
       if (key_info->algorithm == HA_KEY_ALG_LONG_HASH)
-        key_info->algorithm= HA_KEY_ALG_UNDEF;
+        key_info->algorithm= (alter_info->flags & ALTER_CHANGE_COLUMN) ?
+          HA_KEY_ALG_UNDEF : HA_KEY_ALG_HASH;
+      /*
+        This one goes to mysql_prepare_create_table():
+
+            key_info->algorithm= key->key_create_info.algorithm;
+
+        For HA_KEY_ALG_LONG_HASH if we didn't change ANY column, we pass
+        HA_KEY_ALG_HASH to ensure mysql_prepare_create_table() does add_hash_field().
+        This protects fast alter partition from losing hash properties.
+        In case of any column changes we drop algorithm to HA_KEY_ALG_UNDEF and
+        let decide mysql_prepare_create_table() if the hash field is needed
+        depending on new types.
+      */
       key_create_info.algorithm= key_info->algorithm;
       /*
         We copy block size directly as some engines, like Area, sets this