diff --git a/src/libexpr/primops/fetchGit.cc b/src/libexpr/primops/fetchGit.cc
index d866647f0..ca5af7492 100644
--- a/src/libexpr/primops/fetchGit.cc
+++ b/src/libexpr/primops/fetchGit.cc
@@ -174,7 +174,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
     Path tmpDir = createTempDir();
     AutoDelete delTmpDir(tmpDir, true);
 
-    runProgram("tar", true, { "x", "-C", tmpDir }, tar);
+    runProgram("tar", true, { "-x", "-f", "-", "-C", tmpDir }, tar);
 
     gitInfo.storePath = store->addToStore(name, tmpDir);
 
diff --git a/tests/tarball.sh b/tests/tarball.sh
index ba534c626..b2acb9eb9 100644
--- a/tests/tarball.sh
+++ b/tests/tarball.sh
@@ -11,7 +11,7 @@ cp dependencies.nix $tarroot/default.nix
 cp config.nix dependencies.builder*.sh $tarroot/
 
 tarball=$TEST_ROOT/tarball.tar.xz
-(cd $TEST_ROOT && tar c tarball) | xz > $tarball
+(cd $TEST_ROOT && tar cf - tarball) | xz > $tarball
 
 nix-env -f file://$tarball -qa --out-path | grep -q dependencies