--- a/include/the_Foundation/c11threads.h	2026-04-19 00:30:03.038445115 +0200
+++ b/include/the_Foundation/c11threads.h	2026-04-19 00:30:03.069844680 +0200
@@ -31,7 +31,12 @@
 typedef pthread_mutex_t mtx_t;
 typedef pthread_cond_t cnd_t;
 typedef pthread_key_t tss_t;
+#ifndef __once_flag_defined
+#ifndef ONCE_FLAG_INIT
+#define ONCE_FLAG_INIT PTHREAD_ONCE_INIT
+#endif
 typedef pthread_once_t once_flag;
+#endif
 
 typedef int (*thrd_start_t)(void*);
 typedef void (*tss_dtor_t)(void*);
@@ -90,7 +95,9 @@
 
 /* ---- misc ---- */
 
+#ifndef __once_flag_defined
 void call_once(once_flag *flag, void (*func)(void));
+#endif
 
 iEndPublic
 
--- a/src/c11threads.c	2026-04-19 00:30:03.041073068 +0200
+++ b/src/c11threads.c	2026-04-19 00:30:03.069936752 +0200
@@ -35,7 +35,9 @@
 #endif
 #include <time.h>
 
+#ifndef __once_flag_defined
 #define ONCE_FLAG_INIT PTHREAD_ONCE_INIT
+#endif
 
 #ifdef C11THREADS_NO_TIMED_MUTEX
 #  define PTHREAD_MUTEX_TIMED_NP PTHREAD_MUTEX_NORMAL
@@ -184,6 +186,8 @@
 
 void *tss_get(tss_t key) { return pthread_getspecific(key); }
 
+#ifndef __once_flag_defined
 void call_once(once_flag *flag, void (*func)(void)) {
     pthread_once(flag, func);
 }
+#endif
--- a/src/string.c	2026-04-19 00:30:03.043229412 +0200
+++ b/src/string.c	2026-04-19 00:30:03.070124145 +0200
@@ -1196,7 +1196,7 @@
 #if defined(iHaveC11Threads)
     static once_flag inited = ONCE_FLAG_INIT;
 #else
-    static once_flag inited = PTHREAD_ONCE_INIT;
+    static once_flag inited = ONCE_FLAG_INIT;
 #endif
     call_once(&inited, &bufKeyInit);