diff --git a/core/service.go b/core/service.go
index 73b54cf..ac06522 100644
--- a/core/service.go
+++ b/core/service.go
@@ -44,8 +44,18 @@ func (s Service) walker(indexPath map[uint64]*Migration) func(string, os.FileInf
 		}
 
 		name := info.Name()
-		if s.direction != direction.Get(name) {
-			return nil
+		d := direction.Get(name)
+
+		if s.direction == direction.Unknown {
+			// Collect filename of up in case of unknown direction.
+			if d != direction.Up {
+				return nil
+			}
+		} else {
+			// Collect filename of the same direction.
+			if s.direction != d {
+				return nil
+			}
 		}
 
 		fullname := filepath.Clean(filepath.Join(wd, path))
@@ -284,6 +294,8 @@ func (s *Service) NextMigration(name string) (up *Migration, down *Migration, er
 			v := latest.version + 1
 			up.version, down.version = v, v
 		}
+		_, file := filepath.Split(latest.name)
+		verFormat = version.Format(file)
 	}
 
 	// [ver]_[name]_[direction-suffix][.ext]
diff --git a/internal/version/version_test.go b/internal/version/version_test.go
index f99cd00..b2a53f4 100644
--- a/internal/version/version_test.go
+++ b/internal/version/version_test.go
@@ -51,6 +51,9 @@ func TestFormat(t *testing.T) {
 		{value: "", expected: "", message: ""},
 		{value: "foo", expected: "", message: ""},
 		{value: "foo_bar", expected: "", message: ""},
+		{value: "20200101150405_foo", expected: "%d", message: ""},
+		{value: "001_20200101150405_foo", expected: "%03d", message: ""},
+		{value: "999_20200101150405_foo", expected: "%d", message: ""},
 	}
 
 	for _, c := range candidates {
diff --git a/kamimai.go b/kamimai.go
index 6cea8d4..fb8471b 100644
--- a/kamimai.go
+++ b/kamimai.go
@@ -7,7 +7,7 @@ import (
 )
 
 // Version represents kamimai's semantic version.
-const Version = "v0.4.1"
+const Version = "v0.4.2"
 
 // Current returns the current migration version.
 func Current(c *core.Config) (uint64, error) {