diff --git a/tests/fetchMercurial.sh b/tests/fetchMercurial.sh
index 726840664..5c64ffd26 100644
--- a/tests/fetchMercurial.sh
+++ b/tests/fetchMercurial.sh
@@ -7,7 +7,9 @@ fi
 
 clearStore
 
-repo=$TEST_ROOT/hg
+# Intentionally not in a canonical form
+# See https://github.com/NixOS/nix/issues/6195
+repo=$TEST_ROOT/./hg
 
 rm -rf $repo ${repo}-tmp $TEST_HOME/.cache/nix
 
@@ -28,6 +30,12 @@ echo world > $repo/hello
 hg commit --cwd $repo -m 'Bla2'
 rev2=$(hg log --cwd $repo -r tip --template '{node}')
 
+# Fetch an unclean branch.
+echo unclean > $repo/hello
+path=$(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).outPath")
+[[ $(cat $path/hello) = unclean ]]
+hg revert --cwd $repo --all
+
 # Fetch the default branch.
 path=$(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).outPath")
 [[ $(cat $path/hello) = world ]]