diff --git a/mysql-test/r/merge.result b/mysql-test/r/merge.result
index 31edbc0fdce..14308959557 100644
--- a/mysql-test/r/merge.result
+++ b/mysql-test/r/merge.result
@@ -2167,7 +2167,7 @@ col1 int(10) NOT NULL
 ) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 INSERT_METHOD=LAST UNION=(t1);
 insert into m1 (col1) values (1);
 insert into m1 (col1) values (1);
-ERROR 23000: Duplicate entry '' for key '*UNKNOWN*'
+ERROR 23000: Can't write; duplicate key in table 'm1'
 drop table m1, t1;
 #
 # Bug#45800 crash when replacing into a merge table and there is a duplicate
@@ -2204,7 +2204,7 @@ CREATE TABLE m1 (c1 INT, c2 INT, UNIQUE (c1)) ENGINE=MRG_MyISAM INSERT_METHOD=LA
 INSERT INTO m1 VALUES (1,2);
 # insert the duplicate value into the merge table
 INSERT INTO m1 VALUES (3,2);
-ERROR 23000: Duplicate entry '' for key '*UNKNOWN*'
+ERROR 23000: Can't write; duplicate key in table 'm1'
 DROP TABLE m1,t1;
 # Try to define MERGE and MyISAM with keys on different columns
 CREATE TABLE t1 (c1 INT, c2 INT, UNIQUE (c1));
diff --git a/mysql-test/t/merge.test b/mysql-test/t/merge.test
index 0cf37a24f8e..311eb6f12f3 100644
--- a/mysql-test/t/merge.test
+++ b/mysql-test/t/merge.test
@@ -1559,7 +1559,7 @@ CREATE TABLE m1 (
 ) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 INSERT_METHOD=LAST UNION=(t1);
 
 insert into m1 (col1) values (1);
---error ER_DUP_ENTRY
+--error ER_DUP_KEY
 insert into m1 (col1) values (1);
 
 drop table m1, t1;
@@ -1593,7 +1593,7 @@ CREATE TABLE t1 (c1 INT, c2 INT, UNIQUE (c1), UNIQUE (c2));
 CREATE TABLE m1 (c1 INT, c2 INT, UNIQUE (c1)) ENGINE=MRG_MyISAM INSERT_METHOD=LAST UNION=(t1);
 INSERT INTO m1 VALUES (1,2);
 --echo # insert the duplicate value into the merge table
---error ER_DUP_ENTRY
+--error ER_DUP_KEY
 INSERT INTO m1 VALUES (3,2);
 DROP TABLE m1,t1;
 
diff --git a/sql/handler.cc b/sql/handler.cc
index 174034a7eb5..07dc0cf04a9 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -3338,9 +3338,11 @@ void print_keydup_error(TABLE *table, KEY *key, const char *msg, myf errflag)
 
   if (key == NULL)
   {
-    /* Key is unknown */
-    str.copy("", 0, system_charset_info);
-    my_printf_error(ER_DUP_ENTRY, msg, errflag, str.c_ptr(), "*UNKNOWN*");
+    /*
+      Key is unknown. Should only happen if storage engine reports wrong
+      duplicate key number.
+    */
+    my_printf_error(ER_DUP_ENTRY, msg, errflag, "", "*UNKNOWN*");
   }
   else
   {
@@ -3432,11 +3434,9 @@ void handler::print_error(int error, myf errflag)
     if (table)
     {
       uint key_nr=get_dup_key(error);
-      if ((int) key_nr >= 0)
+      if ((int) key_nr >= 0 && key_nr < table->s->keys)
       {
-        print_keydup_error(table,
-                           key_nr == MAX_KEY ? NULL : &table->key_info[key_nr],
-                           errflag);
+        print_keydup_error(table, &table->key_info[key_nr], errflag);
         DBUG_VOID_RETURN;
       }
     }
diff --git a/sql/log_event.cc b/sql/log_event.cc
index b66ceac72bf..dcccdb2527f 100644
--- a/sql/log_event.cc
+++ b/sql/log_event.cc
@@ -4075,8 +4075,13 @@ bool test_if_equal_repl_errors(int expected_error, int actual_error)
     return 1;
   switch (expected_error) {
   case ER_DUP_ENTRY:
+  case ER_DUP_ENTRY_WITH_KEY_NAME:
+  case ER_DUP_KEY:
   case ER_AUTOINC_READ_FAILED:
-    return (actual_error == ER_AUTOINC_READ_FAILED ||
+    return (actual_error == ER_DUP_ENTRY ||
+            actual_error == ER_DUP_ENTRY_WITH_KEY_NAME ||
+            actual_error == ER_DUP_KEY ||
+            actual_error == ER_AUTOINC_READ_FAILED ||
             actual_error == HA_ERR_AUTOINC_ERANGE);
   case ER_UNKNOWN_TABLE:
     return actual_error == ER_IT_IS_A_VIEW;
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 7d37c559e20..2d346a64613 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -9612,12 +9612,13 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
           if ((int) key_nr >= 0)
           {
             const char *err_msg= ER(ER_DUP_ENTRY_WITH_KEY_NAME);
-            if (key_nr == 0 &&
+            if (key_nr == 0 && to->s->keys > 0 &&
                 (to->key_info[0].key_part[0].field->flags &
                  AUTO_INCREMENT_FLAG))
               err_msg= ER(ER_DUP_ENTRY_AUTOINCREMENT_CASE);
-            print_keydup_error(to, key_nr == MAX_KEY ? NULL :
-                                   &to->key_info[key_nr],
+            print_keydup_error(to,
+                               key_nr >= to->s->keys ? NULL :
+                               &to->key_info[key_nr],
                                err_msg, MYF(0));
           }
           else
diff --git a/storage/maria/ma_write.c b/storage/maria/ma_write.c
index 629b774706e..feac1dbf894 100644
--- a/storage/maria/ma_write.c
+++ b/storage/maria/ma_write.c
@@ -340,7 +340,7 @@ err:
       for (j=0 ; j < share->base.keys ; j++)
         maria_flush_bulk_insert(info, j);
     }
-    info->errkey= (int) i;
+    info->errkey= i < share->base.keys ? (int) i : -1;
     /*
       We delete keys in the reverse order of insertion. This is the order that
       a rollback would do and is important for CLR_ENDs generated by