diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
index 49c62df..2c94a27 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
@@ -374,6 +374,7 @@
   private Writer newWriter(HttpServletRequest req, HttpServletResponse res) throws IOException {
     OutputStream out;
     if (acceptsGzipEncoding(req)) {
+      res.addHeader(HttpHeaders.VARY, HttpHeaders.ACCEPT_ENCODING);
       res.setHeader(HttpHeaders.CONTENT_ENCODING, "gzip");
       out = new GZIPOutputStream(res.getOutputStream());
     } else {
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/Renderer.java b/gitiles-servlet/src/main/java/com/google/gitiles/Renderer.java
index 8d04578..694a3c3 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/Renderer.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/Renderer.java
@@ -164,6 +164,7 @@
     res.setCharacterEncoding("UTF-8");
     byte[] data = newRenderer(templateName).setData(soyData).render().getBytes(UTF_8);
     if (BaseServlet.acceptsGzipEncoding(req)) {
+      res.addHeader(HttpHeaders.VARY, HttpHeaders.ACCEPT_ENCODING);
       res.setHeader(HttpHeaders.CONTENT_ENCODING, "gzip");
       data = BaseServlet.gzip(data);
     }
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/doc/DocServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/doc/DocServlet.java
index 8c30e26..6561ada 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/doc/DocServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/doc/DocServlet.java
@@ -202,6 +202,7 @@
     res.setCharacterEncoding(UTF_8.name());
     setCacheHeaders(res);
     if (acceptsGzipEncoding(req)) {
+      res.addHeader(HttpHeaders.VARY, HttpHeaders.ACCEPT_ENCODING);
       res.setHeader(HttpHeaders.CONTENT_ENCODING, "gzip");
       raw = gzip(raw);
     }