diff --git a/db.go b/db.go
index a96a371634dbaaa6e38d0873d0058e13143fd2db..5e21a2ecccfd128818bf48a061318cba85cc3c31 100644
--- a/db.go
+++ b/db.go
@@ -575,6 +575,7 @@ var (
 	_ RawValue    = &rawValue{}
 )
 
+// Default limits for database/sql limit methods.
 var (
 	DefaultConnMaxLifetime = time.Duration(0)
 	DefaultMaxIdleConns    = 0
diff --git a/mysql/mysql.go b/mysql/mysql.go
index 470db3747977cd7722ba193e4928fce20d6d3684..5b6f26dad85518b6d1fbcbb8d1b904ddc909fb65 100644
--- a/mysql/mysql.go
+++ b/mysql/mysql.go
@@ -32,9 +32,9 @@ import (
 )
 
 var (
-	connMaxLifetime time.Duration = db.DefaultConnMaxLifetime
-	maxIdleConns    int           = db.DefaultMaxIdleConns
-	maxOpenConns    int           = db.DefaultMaxOpenConns
+	connMaxLifetime = db.DefaultConnMaxLifetime
+	maxIdleConns    = db.DefaultMaxIdleConns
+	maxOpenConns    = db.DefaultMaxOpenConns
 )
 
 const sqlDriver = `mysql`
diff --git a/postgresql/postgresql.go b/postgresql/postgresql.go
index 0572350a498207aec552e493fc6921dec68ff4a7..e0b87cf9d61518f3f97fdc18a3156b84e4ec02ec 100644
--- a/postgresql/postgresql.go
+++ b/postgresql/postgresql.go
@@ -32,9 +32,9 @@ import (
 )
 
 var (
-	connMaxLifetime time.Duration = db.DefaultConnMaxLifetime
-	maxIdleConns    int           = db.DefaultMaxIdleConns
-	maxOpenConns    int           = db.DefaultMaxOpenConns
+	connMaxLifetime = db.DefaultConnMaxLifetime
+	maxIdleConns    = db.DefaultMaxIdleConns
+	maxOpenConns    = db.DefaultMaxOpenConns
 )
 
 const sqlDriver = `postgres`