diff --git a/plugins/plugins.go b/plugins/plugins.go
index 17f2fe3..05bc03b 100644
--- a/plugins/plugins.go
+++ b/plugins/plugins.go
@@ -22,7 +22,7 @@ type Plugin interface {
 	ConfigureTemplateEngine(*liquid.Engine) error
 	ModifySiteDrop(Site, map[string]interface{}) error
 	PostRead(Site) error
-	PostRender([]byte) []byte
+	PostRender([]byte) ([]byte, error)
 }
 
 // Site is the site interface that is available to a plugin.
@@ -61,7 +61,7 @@ func (p plugin) Initialize(Site) error                             { return nil
 func (p plugin) ConfigureTemplateEngine(*liquid.Engine) error      { return nil }
 func (p plugin) ModifySiteDrop(Site, map[string]interface{}) error { return nil }
 func (p plugin) PostRead(Site) error                               { return nil }
-func (p plugin) PostRender(b []byte) []byte                        { return b }
+func (p plugin) PostRender(b []byte) ([]byte, error)               { return b, nil }
 
 var directory = map[string]Plugin{}
 
@@ -90,11 +90,10 @@ func init() {
 // jemojiPlugin emulates the jekyll-jemoji plugin.
 type jemojiPlugin struct{ plugin }
 
-func (p jemojiPlugin) PostRender(b []byte) []byte {
+func (p jemojiPlugin) PostRender(b []byte) ([]byte, error) {
 	return utils.ApplyToHTMLText(b, func(s string) string {
-		s = emoji.Sprint(s)
-		return s
-	})
+		return emoji.Sprint(s)
+	}), nil
 }
 
 // jekyllMentionsPlugin emulates the jekyll-mentions plugin.
@@ -102,10 +101,10 @@ type jekyllMentionsPlugin struct{ plugin }
 
 var mentionPattern = regexp.MustCompile(`@(\w+)`)
 
-func (p jekyllMentionsPlugin) PostRender(b []byte) []byte {
+func (p jekyllMentionsPlugin) PostRender(b []byte) ([]byte, error) {
 	return utils.ApplyToHTMLText(b, func(s string) string {
 		return mentionPattern.ReplaceAllString(s, `<a href="https://github.com/$1" class="user-mention">@$1</a>`)
-	})
+	}), nil
 }
 
 // jekyllOptionalFrontMatterPlugin emulates the jekyll-optional-front-matter plugin.
diff --git a/site/build.go b/site/build.go
index fad48c7..a4457f1 100644
--- a/site/build.go
+++ b/site/build.go
@@ -44,7 +44,7 @@ func (s *Site) Build() (int, error) {
 	if err := s.setTimeZone(); err != nil {
 		return 0, err
 	}
-	if err := s.prepareRendering(); err != nil {
+	if err := s.ensureRendered(); err != nil {
 		return 0, err
 	}
 	if err := s.Clean(); err != nil {
diff --git a/site/drop.go b/site/drop.go
index f5b588e..2ae76f2 100644
--- a/site/drop.go
+++ b/site/drop.go
@@ -12,7 +12,7 @@ import (
 
 // ToLiquid returns the site variable for template evaluation.
 func (s *Site) ToLiquid() interface{} {
-	s.Do(func() {
+	s.dropOnce.Do(func() {
 		if err := s.initializeDrop(); err != nil {
 			log.Fatalf("ToLiquid failed: %s\n", err)
 		}
@@ -51,16 +51,6 @@ func (s *Site) initializeDrop() error {
 	})
 }
 
-// Render renders the site's pages.
-func (s *Site) Render() error {
-	for _, c := range s.Collections {
-		if err := c.Render(); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
 // The following functions are only used in the drop, therefore they're
 // non-public and they're listed here.
 //
diff --git a/site/errors.go b/site/errors.go
new file mode 100644
index 0000000..1d05dc8
--- /dev/null
+++ b/site/errors.go
@@ -0,0 +1,21 @@
+package site
+
+import (
+	"fmt"
+	"strings"
+)
+
+func combineErrors(errs []error) error {
+	switch len(errs) {
+	case 0:
+		return nil
+	case 1:
+		return errs[0]
+	default:
+		messages := make([]string, len(errs))
+		for i, e := range errs {
+			messages[i] = e.Error()
+		}
+		return fmt.Errorf(strings.Join(messages, "\n"))
+	}
+}
diff --git a/site/render.go b/site/render.go
new file mode 100644
index 0000000..3092ce4
--- /dev/null
+++ b/site/render.go
@@ -0,0 +1,25 @@
+package site
+
+// Render renders the site's pages.
+func (s *Site) Render() error {
+	for _, c := range s.Collections {
+		if err := c.Render(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (s *Site) ensureRendered() (err error) {
+	s.renderOnce.Do(func() {
+		err = s.initializeRenderingPipeline()
+		if err != nil {
+			return
+		}
+		err = s.Render()
+		if err != nil {
+			return
+		}
+	})
+	return
+}
diff --git a/site/site.go b/site/site.go
index 4421936..dee76c6 100644
--- a/site/site.go
+++ b/site/site.go
@@ -20,15 +20,18 @@ type Site struct {
 	Collections []*collection.Collection
 	Routes      map[string]pages.Document // URL path -> Document, only for output pages
 
-	config           config.Config
-	data             map[string]interface{}
-	flags            config.Flags
-	pipeline         *pipelines.Pipeline
-	themeDir         string
-	docs             []pages.Document // all documents, whether or not they are output
-	preparedToRender bool
-	drop             map[string]interface{} // cached drop value
-	sync.Once                               // for computing the drop
+	config   config.Config
+	data     map[string]interface{}
+	flags    config.Flags
+	themeDir string
+
+	docs []pages.Document // all documents, whether or not they are output
+
+	pipeline   *pipelines.Pipeline
+	renderOnce sync.Once
+
+	drop     map[string]interface{} // cached drop value
+	dropOnce sync.Once
 }
 
 // SourceDir returns the site source directory.
diff --git a/site/write.go b/site/write.go
index 382d0f4..c5683a2 100644
--- a/site/write.go
+++ b/site/write.go
@@ -6,7 +6,6 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"strings"
 
 	"github.com/osteele/gojekyll/pages"
 	"github.com/osteele/gojekyll/plugins"
@@ -14,7 +13,6 @@ import (
 )
 
 // WriteFiles writes output files.
-// It attends to options.dry_run.
 func (s *Site) WriteFiles() (count int, err error) {
 	errs := make(chan error)
 	// without this, large sites run out of file descriptors
@@ -40,7 +38,6 @@ func (s *Site) WriteFiles() (count int, err error) {
 }
 
 // WriteDoc writes a document to the destination directory.
-// It attends to options.dry_run.
 func (s *Site) WriteDoc(d pages.Document) error {
 	from := d.SourcePath()
 	rel := d.Permalink()
@@ -69,7 +66,7 @@ func (s *Site) WriteDoc(d pages.Document) error {
 	}
 }
 
-// WriteDocument writes the document to a writer.
+// WriteDocument writes the rendered document.
 func (s *Site) WriteDocument(w io.Writer, d pages.Document) error {
 	switch p := d.(type) {
 	case pages.Page:
@@ -79,9 +76,9 @@ func (s *Site) WriteDocument(w io.Writer, d pages.Document) error {
 	}
 }
 
-// WritePage writes the page to a writer.
+// WritePage writes the rendered page.
 func (s *Site) WritePage(w io.Writer, p pages.Page) error {
-	if err := s.prepareRendering(); err != nil {
+	if err := s.ensureRendered(); err != nil {
 		return err
 	}
 	buf := new(bytes.Buffer)
@@ -89,9 +86,9 @@ func (s *Site) WritePage(w io.Writer, p pages.Page) error {
 		return err
 	}
 	b := buf.Bytes()
-	err := s.runHooks(func(p plugins.Plugin) error {
-		b = p.PostRender(b)
-		return nil
+	err := s.runHooks(func(p plugins.Plugin) (err error) {
+		b, err = p.PostRender(b)
+		return
 	})
 	if err != nil {
 		return err
@@ -99,31 +96,3 @@ func (s *Site) WritePage(w io.Writer, p pages.Page) error {
 	_, err = w.Write(b)
 	return err
 }
-
-func combineErrors(errs []error) error {
-	switch len(errs) {
-	case 0:
-		return nil
-	case 1:
-		return errs[0]
-	default:
-		messages := make([]string, len(errs))
-		for i, e := range errs {
-			messages[i] = e.Error()
-		}
-		return fmt.Errorf(strings.Join(messages, "\n"))
-	}
-}
-
-func (s *Site) prepareRendering() error {
-	if !s.preparedToRender {
-		if err := s.initializeRenderingPipeline(); err != nil {
-			return err
-		}
-		if err := s.Render(); err != nil {
-			return err
-		}
-		s.preparedToRender = true
-	}
-	return nil
-}