Don't depend on git when generating source tarball

local.mk

@@ -1,5 +1,6 @@
 ifeq ($(MAKECMDGOALS), dist)
-  dist-files += $(shell git ls-files)
+  # Make sure we are in repo root with `--git-dir`
+  dist-files += $(shell git --git-dir=.git ls-files || find * -type f)
 endif
 
 dist-files += configure config.h.in nix.spec

release.nix

@@ -36,7 +36,9 @@ let
 
         postUnpack = ''
           # Clean up when building from a working tree.
+          if [[ -d $sourceRoot/.git ]]; then
             git -C $sourceRoot clean -fd
+          fi
         '';
 
         preConfigure = ''