diff --git a/tests/functional/logging.sh b/tests/functional/logging.sh
index 1481b9b36..1ccc21d0b 100644
--- a/tests/functional/logging.sh
+++ b/tests/functional/logging.sh
@@ -15,7 +15,7 @@ nix-build dependencies.nix --no-out-link --compress-build-log
 [ "$(nix-store -l $path)" = FOO ]
 
 # test whether empty logs work fine with `nix log`.
-builder="$(mktemp)"
+builder="$(realpath "$(mktemp)")"
 echo -e "#!/bin/sh\nmkdir \$out" > "$builder"
 outp="$(nix-build -E \
     'with import ./config.nix; mkDerivation { name = "fnord"; builder = '"$builder"'; }' \