diff --git a/mysql-test/r/innodb_ext_key.result b/mysql-test/r/innodb_ext_key.result
index 0b7b042a0b2..4e441245a39 100644
--- a/mysql-test/r/innodb_ext_key.result
+++ b/mysql-test/r/innodb_ext_key.result
@@ -744,5 +744,33 @@ SELECT * FROM t1, t2 WHERE b=a;
 a	b
 set optimizer_switch=@save_optimizer_switch;
 DROP TABLE t1,t2;
+#
+# Bug mdev-3888: INSERT with UPDATE on duplicate keys
+#                with extended_keys=on   
+#
+CREATE TABLE t1 (
+c1 bigint(20) unsigned NOT NULL AUTO_INCREMENT,
+c2 bigint(20) unsigned NOT NULL,
+c3 bigint(20) unsigned NOT NULL,
+c4 varchar(128) DEFAULT NULL,
+PRIMARY KEY (c1),
+UNIQUE KEY uq (c2,c3),
+KEY c3 (c3),
+KEY c4 (c4)
+) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
+set @save_optimizer_switch=@@optimizer_switch;
+set session optimizer_switch='extended_keys=off';
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+DELETE FROM t1;
+set session optimizer_switch='extended_keys=on';
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+set optimizer_switch=@save_optimizer_switch;
+DROP TABLE t1;
 set optimizer_switch=@save_ext_key_optimizer_switch;
 SET SESSION STORAGE_ENGINE=DEFAULT;
diff --git a/mysql-test/t/innodb_ext_key.test b/mysql-test/t/innodb_ext_key.test
index f5b5df527a3..3e82403ddb5 100644
--- a/mysql-test/t/innodb_ext_key.test
+++ b/mysql-test/t/innodb_ext_key.test
@@ -428,5 +428,44 @@ set optimizer_switch=@save_optimizer_switch;
 
 DROP TABLE t1,t2;
 
+
+--echo #
+--echo # Bug mdev-3888: INSERT with UPDATE on duplicate keys
+--echo #                with extended_keys=on   
+--echo #
+
+CREATE TABLE t1 (
+c1 bigint(20) unsigned NOT NULL AUTO_INCREMENT,
+c2 bigint(20) unsigned NOT NULL,
+c3 bigint(20) unsigned NOT NULL,
+c4 varchar(128) DEFAULT NULL,
+PRIMARY KEY (c1),
+UNIQUE KEY uq (c2,c3),
+KEY c3 (c3),
+KEY c4 (c4)
+) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
+
+
+set @save_optimizer_switch=@@optimizer_switch;
+
+set session optimizer_switch='extended_keys=off';
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+  ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+  ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+
+DELETE FROM t1;
+
+set session optimizer_switch='extended_keys=on';
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+  ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
+  ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
+
+set optimizer_switch=@save_optimizer_switch;
+
+DROP TABLE t1;
+
 set optimizer_switch=@save_ext_key_optimizer_switch;
 SET SESSION STORAGE_ENGINE=DEFAULT;
+
diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc
index 3c3b9f85727..231671d172b 100644
--- a/sql/sql_insert.cc
+++ b/sql/sql_insert.cc
@@ -1677,9 +1677,10 @@ int write_record(THD *thd, TABLE *table,COPY_INFO *info)
 	  }
 	}
 	key_copy((uchar*) key,table->record[0],table->key_info+key_nr,0);
+        key_part_map keypart_map= (1 << table->key_info[key_nr].key_parts) - 1;
 	if ((error= (table->file->ha_index_read_idx_map(table->record[1],
                                                         key_nr, (uchar*) key,
-                                                        HA_WHOLE_KEY,
+                                                        keypart_map,
                                                         HA_READ_KEY_EXACT))))
 	  goto err;
       }