diff --git a/src/chunks/writer.odin b/src/chunks/writer.odin
index b4858b3..57101fc 100644
--- a/src/chunks/writer.odin
+++ b/src/chunks/writer.odin
@@ -68,7 +68,7 @@ compute_chunk_path :: proc(
 	err: Error,
 ) {
 
-	@(static) buf: [20]u8
+	buf: [20]u8 // not @(static), that would make it shared across all threads!
 
 	chunk_index_str := strconv.write_int(buf[:], cast(i64)chunk_index, 10)
 	chunk_name := strings.concatenate({CHUNK, chunk_index_str}, allocator)
diff --git a/tests/helpers.odin b/tests/helpers.odin
index 44724f7..b71501f 100644
--- a/tests/helpers.odin
+++ b/tests/helpers.odin
@@ -21,15 +21,19 @@ Test_State :: struct {
 
 test_state_init :: proc(
 	t: ^testing.T,
+	name: string,
 	allocator := context.allocator,
 ) -> Test_State {
 	ensure_dir(t, TEST_INPUT_DIR)
 	ensure_dir(t, TEST_OUTPUT_DIR)
 
-	temp_input_path, err := os.mkdir_temp(TEST_INPUT_DIR, "", allocator)
+	// Use the test name as the pattern so parallel tests with the same
+	// RNG seed generate distinct temp directory names.
+
+	temp_input_path, err := os.mkdir_temp(TEST_INPUT_DIR, name, allocator)
 	testing.expect(t, err == nil, os.error_string(err))
 
-	temp_output_path, err2 := os.mkdir_temp(TEST_OUTPUT_DIR, "", allocator)
+	temp_output_path, err2 := os.mkdir_temp(TEST_OUTPUT_DIR, name, allocator)
 	testing.expect(t, err2 == nil, os.error_string(err2))
 
 	return Test_State {
@@ -59,10 +63,8 @@ test_state_destroy :: proc(
 // -----------------------------------------
 
 ensure_dir :: proc(t: ^testing.T, dir: string) {
-	if !os.exists(dir) {
-		err := os.make_directory_all(dir)
-		testing.expect(t, err == nil, os.error_string(err))
-	}
+	err := os.make_directory_all(dir)
+	testing.expect(t, err == nil || err == .Exist, os.error_string(err)) // TOCTOU safe
 }
 
 create_file :: proc(
@@ -77,10 +79,8 @@ create_file :: proc(
 	defer delete(relpath, allocator)
 
 	dir := os.dir(relpath)
-	if !os.exists(dir) {
-		err2 := os.make_directory_all(dir)
-		testing.expect(t, err2 == nil, os.error_string(err2))
-	}
+	err2 := os.make_directory_all(dir)
+	testing.expect(t, err2 == nil || err2 == .Exist, os.error_string(err2)) // TOCTOU safe
 
 	file, err3 := os.create(relpath)
 	testing.expect(t, err3 == nil, os.error_string(err3))
diff --git a/tests/tests.odin b/tests/tests.odin
index 64e5de3..85e09bc 100644
--- a/tests/tests.odin
+++ b/tests/tests.odin
@@ -6,7 +6,7 @@ import "core:testing"
 single_tiny_file_read_from_chunk :: proc(t: ^testing.T) {
 	// Arrange
 
-	ts := test_state_init(t)
+	ts := test_state_init(t, #procedure)
 	defer test_state_destroy(&ts, t)
 
 	delete_path(&ts, t, "")
@@ -27,7 +27,7 @@ single_tiny_file_read_from_chunk :: proc(t: ^testing.T) {
 single_file_single_chunk_read_from_path :: proc(t: ^testing.T) {
 	// Arrange
 
-	ts := test_state_init(t)
+	ts := test_state_init(t, #procedure)
 	defer test_state_destroy(&ts, t)
 
 	delete_path(&ts, t, "")
@@ -49,7 +49,7 @@ single_file_single_chunk_read_from_path :: proc(t: ^testing.T) {
 multiple_files_single_chunk_read_from_chunk :: proc(t: ^testing.T) {
 	// Arrange
 
-	ts := test_state_init(t)
+	ts := test_state_init(t, #procedure)
 	defer test_state_destroy(&ts, t)
 
 	delete_path(&ts, t, "")
@@ -76,7 +76,7 @@ multiple_files_single_chunk_read_from_chunk :: proc(t: ^testing.T) {
 multiple_files_single_chunk_read_from_path :: proc(t: ^testing.T) {
 	// Arrange
 
-	ts := test_state_init(t)
+	ts := test_state_init(t, #procedure)
 	defer test_state_destroy(&ts, t)
 
 	delete_path(&ts, t, "")