diff --git a/lix/libstore/build/local-derivation-goal.cc b/lix/libstore/build/local-derivation-goal.cc
index 078920a33..db3da2c0a 100644
--- a/lix/libstore/build/local-derivation-goal.cc
+++ b/lix/libstore/build/local-derivation-goal.cc
@@ -72,8 +72,8 @@
 namespace nix {
 
 static kj::Promise<Result<void>> handleDiffHook(
-    uid_t uid,
-    uid_t gid,
+    std::optional<uid_t> uid,
+    std::optional<uid_t> gid,
     const Path & tryA,
     const Path & tryB,
     const Path & drvPath,
@@ -1773,8 +1773,8 @@ try {
                     movePath(actualPath, dst);
 
                     TRY_AWAIT(handleDiffHook(
-                        buildUser ? buildUser->getUID() : getuid(),
-                        buildUser ? buildUser->getGID() : getgid(),
+                        buildUser ? std::optional(buildUser->getUID()) : std::nullopt,
+                        buildUser ? std::optional(buildUser->getGID()) : std::nullopt,
                         finalDestPath,
                         dst,
                         worker.store.printStorePath(drvPath),
diff --git a/tests/functional/check.sh b/tests/functional/check.sh
index ae5671602..2d0969540 100644
--- a/tests/functional/check.sh
+++ b/tests/functional/check.sh
@@ -139,3 +139,11 @@ nix-store -q --references "$obtained" >/dev/null
 nix-build check.nix -A nondeterministic --no-out-link
 nix-build check.nix -A nondeterministic -A hashmismatch --no-out-link --check --keep-going || status=$?
 [ "$status" = "110" ]
+
+
+# basic check that diff hooks are started at all
+STDERR=$(expectStderr 104 nix-build check.nix -A nondeterministic \
+  --diff-hook "$PWD/diff-hook.sh" \
+  --run-diff-hook \
+  --check 2>&1)
+grep "diff-hook ran" <<<"$STDERR"
diff --git a/tests/functional/diff-hook.sh b/tests/functional/diff-hook.sh
new file mode 100755
index 000000000..45de706ac
--- /dev/null
+++ b/tests/functional/diff-hook.sh
@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+echo diff-hook ran