diff --git a/src/libutil/fs-sink.cc b/src/libutil/fs-sink.cc
index b1e342c77..72e5c731f 100644
--- a/src/libutil/fs-sink.cc
+++ b/src/libutil/fs-sink.cc
@@ -68,11 +68,19 @@ static RestoreSinkSettings restoreSinkSettings;
 
 static GlobalConfig::Register r1(&restoreSinkSettings);
 
+static std::filesystem::path append(const std::filesystem::path & src, const CanonPath & path)
+{
+    auto dst = src;
+    if (!path.rel().empty())
+        dst /= path.rel();
+    return dst;
+}
 
 void RestoreSink::createDirectory(const CanonPath & path)
 {
-    if (!std::filesystem::create_directory(dstPath / path.rel()))
-        throw Error("path '%s' already exists", (dstPath / path.rel()).string());
+    auto p = append(dstPath, path);
+    if (!std::filesystem::create_directory(p))
+        throw Error("path '%s' already exists", p.string());
 };
 
 struct RestoreRegularFile : CreateRegularFileSink {
@@ -94,14 +102,6 @@ struct RestoreRegularFile : CreateRegularFileSink {
     void preallocateContents(uint64_t size) override;
 };
 
-static std::filesystem::path append(const std::filesystem::path & src, const CanonPath & path)
-{
-    auto dst = src;
-    if (!path.rel().empty())
-        dst /= path.rel();
-    return dst;
-}
-
 void RestoreSink::createRegularFile(const CanonPath & path, std::function<void(CreateRegularFileSink &)> func)
 {
     auto p = append(dstPath, path);
diff --git a/tests/functional/nars.sh b/tests/functional/nars.sh
index bd2c49fce..4f2470ea7 100755
--- a/tests/functional/nars.sh
+++ b/tests/functional/nars.sh
@@ -11,18 +11,18 @@ rm -rf "$TEST_ROOT/out"
 expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "NAR directory is not sorted"
 
 # Check that nix-store --restore fails if the output already exists.
-expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "path '.*/out/' already exists"
+expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "path '.*/out' already exists"
 
 rm -rf "$TEST_ROOT/out"
 echo foo > "$TEST_ROOT/out"
-expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "cannot create directory.*File exists"
+expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "File exists"
 
 rm -rf "$TEST_ROOT/out"
 ln -s "$TEST_ROOT/out2" "$TEST_ROOT/out"
-expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "cannot create directory.*File exists"
+expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "File exists"
 
 mkdir -p "$TEST_ROOT/out2"
-expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "path '.*/out/' already exists"
+expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "path '.*/out' already exists"
 
 # Check whether restoring and dumping a NAR that contains case
 # collisions is round-tripping, even on a case-insensitive system.