diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index 01d21fa98..0b6db8f0c 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -26,9 +26,9 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
     auto mainUrl = getAttr("url");
     bool unpack = get(drv.env, "unpack").value_or("") == "1";
 
-    /* Note: have to use a fresh downloader here because we're in
+    /* Note: have to use a fresh dataTransfer here because we're in
        a forked process. */
-    auto downloader = makeDownloader();
+    auto dataTransfer = makeDataTransfer();
 
     auto fetch = [&](const std::string & url) {
 
@@ -42,7 +42,7 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
 
             auto decompressor = makeDecompressionSink(
                 unpack && hasSuffix(mainUrl, ".xz") ? "xz" : "none", sink);
-            downloader->download(std::move(request), *decompressor);
+            dataTransfer->download(std::move(request), *decompressor);
             decompressor->finish();
         });
 
diff --git a/src/libstore/datatransfer.cc b/src/libstore/datatransfer.cc
index 9475c24ec..6ea9f9324 100644
--- a/src/libstore/datatransfer.cc
+++ b/src/libstore/datatransfer.cc
@@ -39,7 +39,7 @@ std::string resolveUri(const std::string & uri)
         return uri;
 }
 
-struct CurlDownloader : public Downloader
+struct curlDataTransfer : public DataTransfer
 {
     CURLM * curlm = 0;
 
@@ -48,7 +48,7 @@ struct CurlDownloader : public Downloader
 
     struct DownloadItem : public std::enable_shared_from_this<DownloadItem>
     {
-        CurlDownloader & downloader;
+        curlDataTransfer & dataTransfer;
         DataTransferRequest request;
         DataTransferResult result;
         Activity act;
@@ -72,10 +72,10 @@ struct CurlDownloader : public Downloader
 
         curl_off_t writtenToSink = 0;
 
-        DownloadItem(CurlDownloader & downloader,
+        DownloadItem(curlDataTransfer & dataTransfer,
             const DataTransferRequest & request,
             Callback<DataTransferResult> && callback)
-            : downloader(downloader)
+            : dataTransfer(dataTransfer)
             , request(request)
             , act(*logger, lvlTalkative, actDownload,
                 fmt(request.data ? "uploading '%s'" : "downloading '%s'", request.uri),
@@ -106,7 +106,7 @@ struct CurlDownloader : public Downloader
         {
             if (req) {
                 if (active)
-                    curl_multi_remove_handle(downloader.curlm, req);
+                    curl_multi_remove_handle(dataTransfer.curlm, req);
                 curl_easy_cleanup(req);
             }
             if (requestHeaders) curl_slist_free_all(requestHeaders);
@@ -422,13 +422,13 @@ struct CurlDownloader : public Downloader
                         || writtenToSink == 0
                         || (acceptRanges && encoding.empty())))
                 {
-                    int ms = request.baseRetryTimeMs * std::pow(2.0f, attempt - 1 + std::uniform_real_distribution<>(0.0, 0.5)(downloader.mt19937));
+                    int ms = request.baseRetryTimeMs * std::pow(2.0f, attempt - 1 + std::uniform_real_distribution<>(0.0, 0.5)(dataTransfer.mt19937));
                     if (writtenToSink)
                         warn("%s; retrying from offset %d in %d ms", exc.what(), writtenToSink, ms);
                     else
                         warn("%s; retrying in %d ms", exc.what(), ms);
                     embargo = std::chrono::steady_clock::now() + std::chrono::milliseconds(ms);
-                    downloader.enqueueItem(shared_from_this());
+                    dataTransfer.enqueueItem(shared_from_this());
                 }
                 else
                     fail(exc);
@@ -456,7 +456,7 @@ struct CurlDownloader : public Downloader
 
     std::thread workerThread;
 
-    CurlDownloader()
+    curlDataTransfer()
         : mt19937(rd())
     {
         static std::once_flag globalInit;
@@ -478,7 +478,7 @@ struct CurlDownloader : public Downloader
         workerThread = std::thread([&]() { workerThreadEntry(); });
     }
 
-    ~CurlDownloader()
+    ~curlDataTransfer()
     {
         stopWorkerThread();
 
@@ -676,18 +676,18 @@ struct CurlDownloader : public Downloader
     }
 };
 
-ref<Downloader> getDownloader()
+ref<DataTransfer> getDataTransfer()
 {
-    static ref<Downloader> downloader = makeDownloader();
-    return downloader;
+    static ref<DataTransfer> dataTransfer = makeDataTransfer();
+    return dataTransfer;
 }
 
-ref<Downloader> makeDownloader()
+ref<DataTransfer> makeDataTransfer()
 {
-    return make_ref<CurlDownloader>();
+    return make_ref<curlDataTransfer>();
 }
 
-std::future<DataTransferResult> Downloader::enqueueDataTransfer(const DataTransferRequest & request)
+std::future<DataTransferResult> DataTransfer::enqueueDataTransfer(const DataTransferRequest & request)
 {
     auto promise = std::make_shared<std::promise<DataTransferResult>>();
     enqueueDataTransfer(request,
@@ -701,15 +701,15 @@ std::future<DataTransferResult> Downloader::enqueueDataTransfer(const DataTransf
     return promise->get_future();
 }
 
-DataTransferResult Downloader::download(const DataTransferRequest & request)
+DataTransferResult DataTransfer::download(const DataTransferRequest & request)
 {
     return enqueueDataTransfer(request).get();
 }
 
-void Downloader::download(DataTransferRequest && request, Sink & sink)
+void DataTransfer::download(DataTransferRequest && request, Sink & sink)
 {
     /* Note: we can't call 'sink' via request.dataCallback, because
-       that would cause the sink to execute on the downloader
+       that would cause the sink to execute on the dataTransfer
        thread. If 'sink' is a coroutine, this will fail. Also, if the
        sink is expensive (e.g. one that does decompression and writing
        to the Nix store), it would stall the download thread too much.
diff --git a/src/libstore/datatransfer.hh b/src/libstore/datatransfer.hh
index 53159bdb4..e1c5196e0 100644
--- a/src/libstore/datatransfer.hh
+++ b/src/libstore/datatransfer.hh
@@ -67,11 +67,11 @@ struct DataTransferResult
 
 class Store;
 
-struct Downloader
+struct DataTransfer
 {
-    virtual ~Downloader() { }
+    virtual ~DataTransfer() { }
 
-    /* Enqueue a download request, returning a future to the result of
+    /* Enqueue a data transfer request, returning a future to the result of
        the download. The future may throw a DownloadError
        exception. */
     virtual void enqueueDataTransfer(const DataTransferRequest & request,
@@ -89,18 +89,18 @@ struct Downloader
     enum Error { NotFound, Forbidden, Misc, Transient, Interrupted };
 };
 
-/* Return a shared Downloader object. Using this object is preferred
+/* Return a shared DataTransfer object. Using this object is preferred
    because it enables connection reuse and HTTP/2 multiplexing. */
-ref<Downloader> getDownloader();
+ref<DataTransfer> getDataTransfer();
 
-/* Return a new Downloader object. */
-ref<Downloader> makeDownloader();
+/* Return a new DataTransfer object. */
+ref<DataTransfer> makeDataTransfer();
 
 class DownloadError : public Error
 {
 public:
-    Downloader::Error error;
-    DownloadError(Downloader::Error error, const FormatOrString & fs)
+    DataTransfer::Error error;
+    DownloadError(DataTransfer::Error error, const FormatOrString & fs)
         : Error(fs), error(error)
     { }
 };
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 861287a33..9a19af5e0 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -87,12 +87,12 @@ protected:
         try {
             DataTransferRequest request(cacheUri + "/" + path);
             request.head = true;
-            getDownloader()->download(request);
+            getDataTransfer()->download(request);
             return true;
         } catch (DownloadError & e) {
             /* S3 buckets return 403 if a file doesn't exist and the
                bucket is unlistable, so treat 403 as 404. */
-            if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
+            if (e.error == DataTransfer::NotFound || e.error == DataTransfer::Forbidden)
                 return false;
             maybeDisable();
             throw;
@@ -107,7 +107,7 @@ protected:
         req.data = std::make_shared<string>(data); // FIXME: inefficient
         req.mimeType = mimeType;
         try {
-            getDownloader()->download(req);
+            getDataTransfer()->download(req);
         } catch (DownloadError & e) {
             throw UploadToHTTP("while uploading to HTTP binary cache at '%s': %s", cacheUri, e.msg());
         }
@@ -124,9 +124,9 @@ protected:
         checkEnabled();
         auto request(makeRequest(path));
         try {
-            getDownloader()->download(std::move(request), sink);
+            getDataTransfer()->download(std::move(request), sink);
         } catch (DownloadError & e) {
-            if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
+            if (e.error == DataTransfer::NotFound || e.error == DataTransfer::Forbidden)
                 throw NoSuchBinaryCacheFile("file '%s' does not exist in binary cache '%s'", path, getUri());
             maybeDisable();
             throw;
@@ -142,12 +142,12 @@ protected:
 
         auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
 
-        getDownloader()->enqueueDataTransfer(request,
+        getDataTransfer()->enqueueDataTransfer(request,
             {[callbackPtr, this](std::future<DataTransferResult> result) {
                 try {
                     (*callbackPtr)(result.get().data);
                 } catch (DownloadError & e) {
-                    if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
+                    if (e.error == DataTransfer::NotFound || e.error == DataTransfer::Forbidden)
                         return (*callbackPtr)(std::shared_ptr<std::string>());
                     maybeDisable();
                     callbackPtr->rethrow();
diff --git a/src/nix-prefetch-url/nix-prefetch-url.cc b/src/nix-prefetch-url/nix-prefetch-url.cc
index 58a180e72..4c81e7d82 100644
--- a/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/src/nix-prefetch-url/nix-prefetch-url.cc
@@ -182,7 +182,7 @@ static int _main(int argc, char * * argv)
 
                 DataTransferRequest req(actualUri);
                 req.decompress = false;
-                getDownloader()->download(std::move(req), sink);
+                getDataTransfer()->download(std::move(req), sink);
             }
 
             /* Optionally unpack the file. */
diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index 414689ec5..a4eda90b4 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -139,7 +139,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
 
         // FIXME: use nixos.org?
         auto req = DataTransferRequest(storePathsUrl);
-        auto res = getDownloader()->download(req);
+        auto res = getDataTransfer()->download(req);
 
         auto state = std::make_unique<EvalState>(Strings(), store);
         auto v = state->allocValue();