diff --git a/pkgs/build-support/fetchbzr/builder.sh b/pkgs/build-support/fetchbzr/builder.sh
index 380642a5e681..991864719a07 100644
--- a/pkgs/build-support/fetchbzr/builder.sh
+++ b/pkgs/build-support/fetchbzr/builder.sh
@@ -5,4 +5,4 @@ echo "exporting \`$url' (revision $rev) into \`$out'"
 
 # Perform a lightweight checkout so that we don't end up importing
 # all the repository's history.
-BZR_LOG=/dev/null bzr -Ossl.cert_reqs=none export -r "$rev" --format=dir "$out" "$url"
+XDG_CACHE_HOME="$TMPDIR" BRZ_LOG=/dev/null bzr -Ossl.cert_reqs=none export -r "$rev" --format=dir "$out" "$url"