diff --git a/source/driver.go b/source/driver.go
index 63e6393c3..94bdef317 100644
--- a/source/driver.go
+++ b/source/driver.go
@@ -33,7 +33,7 @@ var drivers = make(map[string]Driver)
 //   * Drivers are supposed to be read only.
 //   * Ideally don't load any contents (into memory) in Open or WithInstance.
 type Driver interface {
-	// Open returns a a new driver instance configured with parameters
+	// Open returns a new driver instance configured with parameters
 	// coming from the URL string. Migrate will call this function
 	// only once per instance.
 	Open(url string) (Driver, error)
diff --git a/source/migration.go b/source/migration.go
index b8bb79020..74f6523cb 100644
--- a/source/migration.go
+++ b/source/migration.go
@@ -66,11 +66,13 @@ func (i *Migrations) Append(m *Migration) (ok bool) {
 }
 
 func (i *Migrations) buildIndex() {
-	i.index = make(uintSlice, 0)
+	i.index = make(uintSlice, 0, len(i.migrations))
 	for version := range i.migrations {
 		i.index = append(i.index, version)
 	}
-	sort.Sort(i.index)
+	sort.Slice(i.index, func(x, y int) bool {
+		return i.index[x] < i.index[y]
+	})
 }
 
 func (i *Migrations) First() (version uint, ok bool) {
@@ -126,18 +128,6 @@ func (i *Migrations) findPos(version uint) int {
 
 type uintSlice []uint
 
-func (s uintSlice) Len() int {
-	return len(s)
-}
-
-func (s uintSlice) Swap(i, j int) {
-	s[i], s[j] = s[j], s[i]
-}
-
-func (s uintSlice) Less(i, j int) bool {
-	return s[i] < s[j]
-}
-
 func (s uintSlice) Search(x uint) int {
 	return sort.Search(len(s), func(i int) bool { return s[i] >= x })
 }