diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index f26ee811b..5cb0dac17 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -311,6 +311,19 @@ void InputScheme::clone(const Input & input, const Path & destDir)
     throw Error("do not know how to clone input '%s'", input.to_string());
 }
 
+std::pair<StorePath, Input> InputScheme::fetch(ref<Store> store, const Input & input)
+{
+    auto [accessor, input2] = lazyFetch(store, input);
+
+    auto source = sinkToSource([&](Sink & sink) {
+        accessor->dumpPath(CanonPath::root, sink);
+    });
+
+    auto storePath = store->addToStoreFromDump(*source, "source");
+
+    return {storePath, input2};
+}
+
 std::pair<ref<InputAccessor>, Input> InputScheme::lazyFetch(ref<Store> store, const Input & input)
 {
     auto [storePath, input2] = fetch(store, input);
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 9c67217ee..6ca798b71 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -135,7 +135,11 @@ struct InputScheme
 
     virtual void markChangedFile(const Input & input, std::string_view file, std::optional<std::string> commitMsg);
 
-    virtual std::pair<StorePath, Input> fetch(ref<Store> store, const Input & input) = 0;
+    /* Note: the default implementations of fetch() and lazyFetch()
+       are defined using the other, so implementations have to
+       override at least one. */
+
+    virtual std::pair<StorePath, Input> fetch(ref<Store> store, const Input & input);
 
     virtual std::pair<ref<InputAccessor>, Input> lazyFetch(ref<Store> store, const Input & input);
 
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 93138398a..da115478e 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -134,7 +134,9 @@ struct GitArchiveInputScheme : InputScheme
 
     bool hasAllInfo(const Input & input) override
     {
-        return input.getRev() && maybeGetIntAttr(input.attrs, "lastModified");
+        return input.getRev() &&
+            true; // FIXME
+            //maybeGetIntAttr(input.attrs, "lastModified");
     }
 
     Input applyOverrides(
@@ -224,11 +226,6 @@ struct GitArchiveInputScheme : InputScheme
         return {res.storePath, input};
     }
 
-    std::pair<StorePath, Input> fetch(ref<Store> store, const Input & _input) override
-    {
-        throw UnimplementedError("GitArchive::fetch()");
-    }
-
     std::pair<ref<InputAccessor>, Input> lazyFetch(ref<Store> store, const Input & input) override
     {
         auto [storePath, input2] = downloadArchive(store, input);