diff --git a/libretro-common/rthreads/rthreads.c b/libretro-common/rthreads/rthreads.c
index ff11978668..2a748edd53 100644
--- a/libretro-common/rthreads/rthreads.c
+++ b/libretro-common/rthreads/rthreads.c
@@ -22,9 +22,11 @@
 
 #ifdef __unix__
 #ifndef __sun__
+#ifndef _POSIX_C_SOURCE
 #define _POSIX_C_SOURCE 199309
 #endif
 #endif
+#endif
 
 #include <stdlib.h>
 #include <string.h>