diff --git a/mysql-test/r/alter_table_trans.result b/mysql-test/r/alter_table_trans.result
index 3dd5c00d3d8..67ae4075d57 100644
--- a/mysql-test/r/alter_table_trans.result
+++ b/mysql-test/r/alter_table_trans.result
@@ -4,3 +4,15 @@ ALTER TABLE t1 RENAME TO t2, DISABLE KEYS;
 Warnings:
 Note	1031	Table storage engine for 't1' doesn't have this option
 DROP TABLE t2;
+CREATE TABLE t1 (
+col4 text NOT NULL,
+col2 int(11) NOT NULL DEFAULT '0',
+col3 int(11) DEFAULT NULL,
+extra int(11) DEFAULT NULL,
+KEY idx (col4(10))
+) ENGINE=InnoDB DEFAULT CHARSET=latin1;
+insert t1 values (repeat('1', 8193),3,1,1);
+insert t1 values (repeat('3', 8193),3,1,1);
+ALTER TABLE t1 ADD PRIMARY KEY (col4(10)) , ADD UNIQUE KEY uidx (col3);
+ERROR 23000: Duplicate entry '1' for key 'uidx'
+DROP TABLE t1;
diff --git a/mysql-test/t/alter_table_trans.test b/mysql-test/t/alter_table_trans.test
index 9096a392af4..29b9b4c212f 100644
--- a/mysql-test/t/alter_table_trans.test
+++ b/mysql-test/t/alter_table_trans.test
@@ -13,3 +13,23 @@ drop table if exists t1,t2;
 CREATE TABLE t1 (a INT, INDEX(a)) engine=innodb;
 ALTER TABLE t1 RENAME TO t2, DISABLE KEYS;
 DROP TABLE t2;
+
+#
+# MDEV-5406 add index to an innodb table with a uniqueness violation crashes mysqld
+#
+
+CREATE TABLE t1 (
+  col4 text NOT NULL,
+  col2 int(11) NOT NULL DEFAULT '0',
+  col3 int(11) DEFAULT NULL,
+  extra int(11) DEFAULT NULL,
+  KEY idx (col4(10))
+) ENGINE=InnoDB DEFAULT CHARSET=latin1;
+
+insert t1 values (repeat('1', 8193),3,1,1);
+insert t1 values (repeat('3', 8193),3,1,1);
+--error ER_DUP_ENTRY
+ALTER TABLE t1 ADD PRIMARY KEY (col4(10)) , ADD UNIQUE KEY uidx (col3);
+DROP TABLE t1;
+
+
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index eda178fcc64..c9f754a204f 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -6893,14 +6893,35 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
         /* Only report error if handler has not already reported an error */
         if (!thd->is_error())
         {
-        /*
-          Exchange the key_info for the error message. If we exchange
-          key number by key name in the message later, we need correct info.
-        */
-        KEY *save_key_info= table->key_info;
-        table->key_info= key_info;
-        table->file->print_error(error, MYF(0));
-        table->key_info= save_key_info;
+          /*
+            HACK HACK HACK
+            Prepare the list of keys for an error message.
+            It must match what the engine does internally in ::add_index().
+            Here we emulate what innobase_create_key_def() does.
+            Luckily, in 10.0 this will go away.
+          */
+          KEY *save_key_info= table->key_info;
+          uint add_cnt= index_add_count, old_cnt= table->s->keys;
+          KEY *merged= (KEY*)thd->alloc((old_cnt + add_cnt) * sizeof(KEY));
+#define is_PK(K) (!my_strcasecmp(system_charset_info, (K)->name, "PRIMARY"))
+
+          if (is_PK(key_info))
+          {
+            merged[0]= key_info[0];
+            if (is_PK(table->key_info))
+            {
+              old_cnt--;
+              table->key_info++;
+            }
+            memcpy(merged + 1, table->key_info, old_cnt * sizeof(KEY));
+            memcpy(merged + old_cnt + 1, key_info + 1, (add_cnt - 1) * sizeof(KEY));
+          }
+          else
+            merged= key_info;
+
+          table->key_info= merged;
+          table->file->print_error(error, MYF(0));
+          table->key_info= save_key_info;
         }
         goto err_new_table_cleanup;
       }