diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index 31db7a47d6d..16f1c9fce82 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -133,6 +133,7 @@ const (
 	LevelLinearizable
 )
 
+// String returns the name of the transaction isolation level.
 func (i IsolationLevel) String() string {
 	switch i {
 	case LevelDefault: