diff --git a/src/libstore/download.hh b/src/libstore/download.hh
index 0a278a05e..d9d525d4e 100644
--- a/src/libstore/download.hh
+++ b/src/libstore/download.hh
@@ -21,8 +21,8 @@ struct DownloadRequest
     std::shared_ptr<std::string> data;
     std::string mimeType;
 
-    DownloadRequest(const std::string & uri, std::shared_ptr<std::string> data = nullptr, std::string mimeType = "")
-        : uri(uri), parentAct(curActivity), data(std::move(data)), mimeType(std::move(mimeType)) { }
+    DownloadRequest(const std::string & uri)
+        : uri(uri), parentAct(curActivity) { }
 };
 
 struct DownloadResult
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 93bd3e5d5..b9e9cd5da 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -38,7 +38,7 @@ public:
             try {
                 BinaryCacheStore::init();
             } catch (UploadToHTTP &) {
-                throw Error(format("'%s' does not appear to be a binary cache") % cacheUri);
+                throw Error("'%s' does not appear to be a binary cache", cacheUri);
             }
             diskCache->createCache(cacheUri, storeDir, wantMassQuery_, priority);
         }
@@ -67,8 +67,9 @@ protected:
         const std::string & data,
         const std::string & mimeType) override
     {
-        auto data_ = std::make_shared<string>(data);
-        auto req = DownloadRequest(cacheUri + "/" + path, data_, mimeType);
+        auto req = DownloadRequest(cacheUri + "/" + path);
+        req.data = std::make_shared<string>(data); // FIXME: inefficient
+        req.mimeType = mimeType;
         try {
             getDownloader()->download(req);
         } catch (DownloadError & e) {