diff --git a/cache/downloader.go b/cache/downloader.go
index be4bdb1..f3c2191 100644
--- a/cache/downloader.go
+++ b/cache/downloader.go
@@ -1,7 +1,6 @@
 package cache
 
 import (
-	"errors"
 	"io"
 	"net/http"
 	"os"
@@ -9,6 +8,16 @@ import (
 	"sync"
 )
 
+// DownloadError conveys information about a download request that failed.
+type DownloadError struct {
+	Status string
+}
+
+// Error returns a description of the error.
+func (d *DownloadError) Error() string {
+	return d.Status
+}
+
 // downloader attempts to download a file from a remote URL.
 type downloader struct {
 	doneMutex  sync.Mutex
@@ -40,7 +49,9 @@ func newDownloader(rawurl, jsonFilename, dataFilename string) *downloader {
 		}
 		defer resp.Body.Close()
 		if resp.StatusCode != 200 {
-			d.err = errors.New(resp.Status)
+			d.err = &DownloadError{
+				Status: resp.Status,
+			}
 			return
 		}
 		f, err := os.Create(dataFilename)
diff --git a/server.go b/server.go
index b34daef..b6d935b 100644
--- a/server.go
+++ b/server.go
@@ -48,8 +48,6 @@ func (s *Server) writeHeaders(w http.ResponseWriter, e *cache.Entry) {
 	w.WriteHeader(http.StatusOK)
 }
 
-// TODO: support for HEAD requests
-
 // ServeHTTP processes an incoming request to the proxy. GET requests are
 // served with the storage backend and every other request is (out of
 // necessity) rejected since it can't be cached.
@@ -67,7 +65,11 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	defer r.Close()
 	e, err := r.GetEntry()
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		if dErr, ok := err.(*cache.DownloadError); ok {
+			http.Error(w, dErr.Error(), http.StatusServiceUnavailable)
+		} else {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+		}
 		log.Println("[ERR]", err)
 		return
 	}