diff --git a/ast.go b/ast.go
index 966e4a9..0286a24 100644
--- a/ast.go
+++ b/ast.go
@@ -15,47 +15,58 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
-var (
-	astFields = make(map[string]map[string]map[string]*structtag.Tags) // map proto file with proto message ast struct
-)
+var astFields = make(map[string]map[string]map[string]*structtag.Tags) // map proto file with proto message ast struct
+
+func (g *Generator) astFill(file *protogen.File, message *protogen.Message) error {
+	for _, field := range message.Fields {
+		if field.Desc.Options() == nil {
+			continue
+		}
+		if !proto.HasExtension(field.Desc.Options(), tag_options.E_Tags) {
+			continue
+		}
+
+		opts := proto.GetExtension(field.Desc.Options(), tag_options.E_Tags)
+		if opts != nil {
+			fpath := filepath.Join(g.tagPath, file.GeneratedFilenamePrefix+".pb.go")
+			mp, ok := astFields[fpath]
+			if !ok {
+				mp = make(map[string]map[string]*structtag.Tags)
+			}
+			nmp, ok := mp[message.GoIdent.GoName]
+			if !ok {
+				nmp = make(map[string]*structtag.Tags)
+			}
+			tags, err := structtag.Parse(opts.(string))
+			if err != nil {
+				return err
+			}
+			nmp[field.GoName] = tags
+			mp[message.GoIdent.GoName] = nmp
+			astFields[fpath] = mp
+		}
+	}
+	for _, nmessage := range message.Messages {
+		if err := g.astFill(file, nmessage); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
 
 func (g *Generator) astGenerate(plugin *protogen.Plugin) error {
 	if g.tagPath == "" {
 		return nil
 	}
+
 	for _, file := range plugin.Files {
 		if !file.Generate {
 			continue
 		}
-
 		for _, message := range file.Messages {
-			for _, field := range message.Fields {
-				if field.Desc.Options() == nil {
-					continue
-				}
-				if !proto.HasExtension(field.Desc.Options(), tag_options.E_Tags) {
-					continue
-				}
-
-				opts := proto.GetExtension(field.Desc.Options(), tag_options.E_Tags)
-				if opts != nil {
-					fpath := filepath.Join(g.tagPath, file.GeneratedFilenamePrefix+".pb.go")
-					mp, ok := astFields[fpath]
-					if !ok {
-						mp = make(map[string]map[string]*structtag.Tags)
-					}
-					nmp, ok := mp[message.GoIdent.GoName]
-					if !ok {
-						nmp = make(map[string]*structtag.Tags)
-					}
-					tags, err := structtag.Parse(opts.(string))
-					if err != nil {
-						return err
-					}
-					nmp[field.GoName] = tags
-					mp[message.GoIdent.GoName] = nmp
-					astFields[fpath] = mp
-				}
+			if err := g.astFill(file, message); err != nil {
+				return err
 			}
 		}
 	}