diff --git a/mysql-test/r/innodb_mysql.result b/mysql-test/r/innodb_mysql.result
index 2c14b1f2385..a348c63ec81 100644
--- a/mysql-test/r/innodb_mysql.result
+++ b/mysql-test/r/innodb_mysql.result
@@ -1677,3 +1677,87 @@ select @@session.sql_log_bin, @@session.binlog_format, @@session.tx_isolation;
 CREATE TABLE t1 ( a INT ) ENGINE=InnoDB;
 INSERT INTO t1 VALUES(1);
 DROP TABLE t1;
+CREATE TABLE foo (a int, b int, c char(10),
+PRIMARY KEY (c(3)),
+KEY b (b)
+) engine=innodb;
+CREATE TABLE foo2 (a int, b int, c char(10),
+PRIMARY KEY (c),
+KEY b (b)
+) engine=innodb;
+CREATE TABLE bar (a int, b int, c char(10),
+PRIMARY KEY (c(3)),
+KEY b (b)
+) engine=myisam;
+INSERT INTO foo VALUES
+(1,2,'abcdefghij'), (2,3,''), (3,4,'klmnopqrst'),
+(4,5,'uvwxyz'), (5,6,'meotnsyglt'), (4,5,'asfdewe');
+INSERT INTO bar SELECT * FROM foo;
+INSERT INTO foo2 SELECT * FROM foo;
+EXPLAIN SELECT c FROM bar WHERE b>2;;
+id	1
+select_type	SIMPLE
+table	bar
+type	ALL
+possible_keys	b
+key	NULL
+key_len	NULL
+ref	NULL
+rows	6
+Extra	Using where
+EXPLAIN SELECT c FROM foo WHERE b>2;;
+id	1
+select_type	SIMPLE
+table	foo
+type	ALL
+possible_keys	b
+key	NULL
+key_len	NULL
+ref	NULL
+rows	6
+Extra	Using where
+EXPLAIN SELECT c FROM foo2 WHERE b>2;;
+id	1
+select_type	SIMPLE
+table	foo2
+type	range
+possible_keys	b
+key	b
+key_len	5
+ref	NULL
+rows	3
+Extra	Using where; Using index
+EXPLAIN SELECT c FROM bar WHERE c>2;;
+id	1
+select_type	SIMPLE
+table	bar
+type	ALL
+possible_keys	PRIMARY
+key	NULL
+key_len	NULL
+ref	NULL
+rows	6
+Extra	Using where
+EXPLAIN SELECT c FROM foo WHERE c>2;;
+id	1
+select_type	SIMPLE
+table	foo
+type	ALL
+possible_keys	PRIMARY
+key	NULL
+key_len	NULL
+ref	NULL
+rows	6
+Extra	Using where
+EXPLAIN SELECT c FROM foo2 WHERE c>2;;
+id	1
+select_type	SIMPLE
+table	foo2
+type	index
+possible_keys	PRIMARY
+key	b
+key_len	5
+ref	NULL
+rows	6
+Extra	Using where; Using index
+DROP TABLE foo, bar, foo2;
diff --git a/mysql-test/t/innodb_mysql.test b/mysql-test/t/innodb_mysql.test
index ed8de208474..06ebb079a1b 100644
--- a/mysql-test/t/innodb_mysql.test
+++ b/mysql-test/t/innodb_mysql.test
@@ -43,3 +43,39 @@ CREATE TABLE t1 ( a INT ) ENGINE=InnoDB;
 INSERT INTO t1 VALUES(1);
 DROP TABLE t1;
 
+#
+# Bug #37742: HA_EXTRA_KEYREAD flag is set when key contains only prefix of
+# requested column
+#
+
+CREATE TABLE foo (a int, b int, c char(10),
+                  PRIMARY KEY (c(3)),
+                  KEY b (b)
+) engine=innodb;
+
+CREATE TABLE foo2 (a int, b int, c char(10),
+                  PRIMARY KEY (c),
+                  KEY b (b)
+) engine=innodb;
+
+CREATE TABLE bar (a int, b int, c char(10),
+                  PRIMARY KEY (c(3)),
+                  KEY b (b)
+) engine=myisam;
+
+INSERT INTO foo VALUES
+   (1,2,'abcdefghij'), (2,3,''), (3,4,'klmnopqrst'),
+   (4,5,'uvwxyz'), (5,6,'meotnsyglt'), (4,5,'asfdewe');
+
+INSERT INTO bar SELECT * FROM foo;
+INSERT INTO foo2 SELECT * FROM foo;
+
+--query_vertical EXPLAIN SELECT c FROM bar WHERE b>2;
+--query_vertical EXPLAIN SELECT c FROM foo WHERE b>2;
+--query_vertical EXPLAIN SELECT c FROM foo2 WHERE b>2;
+
+--query_vertical EXPLAIN SELECT c FROM bar WHERE c>2;
+--query_vertical EXPLAIN SELECT c FROM foo WHERE c>2;
+--query_vertical EXPLAIN SELECT c FROM foo2 WHERE c>2;
+
+DROP TABLE foo, bar, foo2;
diff --git a/sql/table.cc b/sql/table.cc
index 89714e4e47e..1de47a48513 100644
--- a/sql/table.cc
+++ b/sql/table.cc
@@ -1416,7 +1416,9 @@ static int open_binary_frm(THD *thd, TABLE_SHARE *share, uchar *head,
           */
           if (ha_option & HA_PRIMARY_KEY_IN_READ_INDEX)
           {
-            field->part_of_key= share->keys_in_use;
+            if (field->key_length() == key_part->length &&
+                !(field->flags & BLOB_FLAG))
+              field->part_of_key= share->keys_in_use;
             if (field->part_of_sortkey.is_set(key))
               field->part_of_sortkey= share->keys_in_use;
           }