diff --git a/golang/token_determinant.go b/golang/token_determinant.go
index 5451487..370c302 100644
--- a/golang/token_determinant.go
+++ b/golang/token_determinant.go
@@ -22,7 +22,10 @@ func ID(arg string) *Tokens {
 }
 
 func (v *Tokens) Pkg(arg string) *Tokens {
-	*v = append(*v, &models.Keyword{D: arg, Verify: true})
+	if len(arg) == 0 {
+		return v
+	}
+	*v = append(*v, &models.Raw{D: arg, Verify: true})
 	return v.Op(".")
 }
 
diff --git a/internal/models/letter.go b/internal/models/letter.go
index 1c84a86..7cd9446 100644
--- a/internal/models/letter.go
+++ b/internal/models/letter.go
@@ -6,6 +6,7 @@
 package models
 
 import (
+	"fmt"
 	"io"
 
 	"go.osspkg.com/gogen/internal/gen"
@@ -21,12 +22,16 @@ func (v *Letter) Render(w io.Writer) error {
 }
 
 type Raw struct {
-	D  string
-	T  types.Token
-	AT []types.Token
+	D      string
+	T      types.Token
+	AT     []types.Token
+	Verify bool
 }
 
 func (v *Raw) Render(w io.Writer) error {
+	if v.Verify && !rexLetter.MatchString(v.D) {
+		return fmt.Errorf("invalid letter: %s", v.D)
+	}
 	if err := gen.Render(w, v.D); err != nil {
 		return err
 	}