diff --git a/src/libfetchers/git-utils.cc b/src/libfetchers/git-utils.cc
index fb5341599..59b4d424a 100644
--- a/src/libfetchers/git-utils.cc
+++ b/src/libfetchers/git-utils.cc
@@ -170,6 +170,11 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
 {
     /** Location of the repository on disk. */
     std::filesystem::path path;
+    /**
+     * libgit2 repository. Note that new objects are not written to disk,
+     * because we are using a mempack backend. For writing to disk, see
+     * `flush()`, which is also called by `GitFileSystemObjectSink::sync()`.
+     */
     Repository repo;
     /**
      * In-memory object store for efficient batched writing to packfiles.
@@ -1064,7 +1069,7 @@ struct GitFileSystemObjectSinkImpl : GitFileSystemObjectSink
             git_tree_entry_filemode(entry));
     }
 
-    Hash sync() override
+    Hash flush() override
     {
         updateBuilders({});
 
diff --git a/src/libfetchers/git-utils.hh b/src/libfetchers/git-utils.hh
index 65a598ce5..f45b5a504 100644
--- a/src/libfetchers/git-utils.hh
+++ b/src/libfetchers/git-utils.hh
@@ -7,12 +7,16 @@ namespace nix {
 
 namespace fetchers { struct PublicKey; }
 
+/**
+ * A sink that writes into a Git repository. Note that nothing may be written
+ * until `flush()` is called.
+ */
 struct GitFileSystemObjectSink : ExtendedFileSystemObjectSink
 {
     /**
      * Flush builder and return a final Git hash.
      */
-    virtual Hash sync() = 0;
+    virtual Hash flush() = 0;
 };
 
 struct GitRepo
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index ecfd035fc..308cff33a 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -261,7 +261,7 @@ struct GitArchiveInputScheme : InputScheme
         auto tarballCache = getTarballCache();
         auto parseSink = tarballCache->getFileSystemObjectSink();
         auto lastModified = unpackTarfileToSink(archive, *parseSink);
-        auto tree = parseSink->sync();
+        auto tree = parseSink->flush();
 
         act.reset();
 
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index a082b0078..aa5d61bc5 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -170,7 +170,7 @@ static DownloadTarballResult downloadTarball_(
     auto tarballCache = getTarballCache();
     auto parseSink = tarballCache->getFileSystemObjectSink();
     auto lastModified = unpackTarfileToSink(archive, *parseSink);
-    auto tree = parseSink->sync();
+    auto tree = parseSink->flush();
 
     act.reset();
 
diff --git a/tests/unit/libfetchers/git-utils.cc b/tests/unit/libfetchers/git-utils.cc
index de5110cc3..0bf3076dc 100644
--- a/tests/unit/libfetchers/git-utils.cc
+++ b/tests/unit/libfetchers/git-utils.cc
@@ -77,7 +77,7 @@ TEST_F(GitUtilsTest, sink_basic)
 
     // sink->createHardlink("foo-1.1/links/foo-2", CanonPath("foo-1.1/hello"));
 
-    auto result = repo->dereferenceSingletonDirectory(sink->sync());
+    auto result = repo->dereferenceSingletonDirectory(sink->flush());
     auto accessor = repo->getAccessor(result, false);
     auto entries = accessor->readDirectory(CanonPath::root);
     ASSERT_EQ(entries.size(), 5);