diff --git a/src/ui.c b/src/ui.c
index 605b495..3cd5699 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -11,6 +11,7 @@
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
+#define _POSIX_THREAD_SAFE_FUNCTIONS
 #include <time.h>
 #include <time.h>
 #if defined(_MSC_VER)