diff --git a/nix/t1/run/run-vcs-emu.nix b/nix/t1/run/run-vcs-emu.nix
index cb7ca0a6d..58617e28c 100644
--- a/nix/t1/run/run-vcs-emu.nix
+++ b/nix/t1/run/run-vcs-emu.nix
@@ -49,6 +49,8 @@ stdenvNoCC.mkDerivation (rec {
   ++ lib.optionals emulator.enableCover [
     "-cm"
     "assert"
+    "-assert"
+    "hier=${testCase}/${testCase.pname}.cover"
   ]
   ++ lib.optionals emulator.enableTrace [
     "+t1_wave_path=${testCase.pname}.fsdb"