diff --git a/test/testing_darwinunix.c b/test/testing_darwinunix.c
index 7fa42b4f..4ce32e06 100644
--- a/test/testing_darwinunix.c
+++ b/test/testing_darwinunix.c
@@ -1,4 +1,8 @@
 // 28 april 2019
+// TODO pin down minimum POSIX versions (depends on what macOS 10.8 conforms to and what GLib/GTK+ require)
+// TODO feature test macros for things like monotonic clocks?
+// TODO is this needed in this file specifically, or just in testing_unix.c?
+#define _POSIX_C_SOURCE 200112L
 #include <errno.h>
 #include <inttypes.h>
 #include <setjmp.h>
diff --git a/test/testing_unix.c b/test/testing_unix.c
index 2e22fdf5..a6719b88 100644
--- a/test/testing_unix.c
+++ b/test/testing_unix.c
@@ -1,4 +1,5 @@
 // 23 april 2019
+#define _POSIX_C_SOURCE 200112L
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>