diff --git a/libretro-common/rthreads/rthreads.c b/libretro-common/rthreads/rthreads.c
index ae52cc57a1..a49c485242 100644
--- a/libretro-common/rthreads/rthreads.c
+++ b/libretro-common/rthreads/rthreads.c
@@ -21,8 +21,10 @@
  */
 
 #ifdef __unix__
+#ifndef __sun__
 #define _POSIX_C_SOURCE 199309
 #endif
+#endif
 
 #include <stdlib.h>