diff --git a/tests/test_osrs_puffer_render.py b/tests/test_osrs_puffer_render.py
index 8842894b1e..b551f669df 100644
--- a/tests/test_osrs_puffer_render.py
+++ b/tests/test_osrs_puffer_render.py
@@ -84,6 +84,7 @@ def test_puf_render_owns_renderer_lifecycle(tmp_path: Path, wrapper: str) -> Non
     subprocess.run(
         [
             compiler,
+            "-D_POSIX_C_SOURCE=200809L",
             "-std=c11",
             "-I",
             str(REPOSITORY_ROOT),