--- src/debug.c	2024-11-08 13:08:06.174085089 +0100
+++ src/debug.c	2024-11-08 13:11:43.133601548 +0100
@@ -152,8 +152,10 @@
 #ifdef HAVE_W32_SYSTEM
   thread = (uintptr_t)GetCurrentThreadId ();
 #elif defined(__linux)
+#ifdef SYS_gettid
   thread = (uintptr_t)gettid ();
 #endif
+#endif
   if (sizeof (thread) < len)
     {
       int zerolen = len;