diff --git a/templates.go b/templates.go
index 6314c28..ff00ee7 100644
--- a/templates.go
+++ b/templates.go
@@ -9,50 +9,69 @@ import (
 	pathpkg "path"
 	"strings"
 	"text/template"
-	"text/template/parse"
 )
 
 // Template represents a template.
 type Template interface {
-	AddParseTree(*parse.Tree) error
+	Clone() (Template, error)
+	AddTemplates(Template) error
 	Execute(io.Writer, interface{}) error
-	Tree() *parse.Tree
 }
 
 type textTemplate struct {
 	tmpl *template.Template
 }
 
-func (t textTemplate) AddParseTree(tree *parse.Tree) error {
-	_, err := t.tmpl.AddParseTree(t.tmpl.Name(), tree)
-	return err
+func (t textTemplate) Clone() (Template, error) {
+	clone, err := t.tmpl.Clone()
+	return textTemplate{clone}, err
+}
+
+func (t textTemplate) AddTemplates(other Template) error {
+	otherTmpl := other.(textTemplate).tmpl
+	for _, def := range otherTmpl.Templates() {
+		if def.Name() == otherTmpl.Name() {
+			continue
+		}
+		_, err := t.tmpl.AddParseTree(def.Name(), def.Tree)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (t textTemplate) Execute(w io.Writer, data interface{}) error {
 	return t.tmpl.Execute(w, data)
 }
 
-func (t textTemplate) Tree() *parse.Tree {
-	return t.tmpl.Tree
-}
-
 type htmlTemplate struct {
 	tmpl *htemplate.Template
 }
 
-func (t htmlTemplate) AddParseTree(tree *parse.Tree) error {
-	_, err := t.tmpl.AddParseTree(t.tmpl.Name(), tree)
-	return err
+func (t htmlTemplate) Clone() (Template, error) {
+	clone, err := t.tmpl.Clone()
+	return htmlTemplate{clone}, err
+}
+
+func (t htmlTemplate) AddTemplates(other Template) error {
+	otherTmpl := other.(htmlTemplate).tmpl
+	for _, def := range otherTmpl.Templates() {
+		if def.Name() == otherTmpl.Name() {
+			continue
+		}
+		_, err := t.tmpl.AddParseTree(def.Name(), def.Tree)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (t htmlTemplate) Execute(w io.Writer, data interface{}) error {
 	return t.tmpl.Execute(w, data)
 }
 
-func (t htmlTemplate) Tree() *parse.Tree {
-	return t.tmpl.Tree
-}
-
 // Templates contains site templates.
 type Templates struct {
 	tmpls map[string]Template
@@ -129,12 +148,20 @@ func (t *Templates) Load(dir string, exts []string) error {
 		if _, ok := extsMap[ext]; !ok {
 			continue
 		}
-		base := pathpkg.Join(pathpkg.Dir(path), "base"+ext)
-		if tmpl, ok := t.tmpls[base]; ok {
-			err := t.tmpls[path].AddParseTree(tmpl.Tree())
+		basePath := pathpkg.Join(pathpkg.Dir(path), "base"+ext)
+		if path == basePath {
+			continue
+		}
+		if base, ok := t.tmpls[basePath]; ok {
+			tmpl, err := base.Clone()
 			if err != nil {
 				return err
 			}
+			// Load customized template definitions
+			if err := tmpl.AddTemplates(t.tmpls[path]); err != nil {
+				return err
+			}
+			t.tmpls[path] = tmpl
 		}
 	}
 	return nil