diff --git a/src/fmacros.h b/src/fmacros.h
index c16f5e20..44e378a6 100644
--- a/src/fmacros.h
+++ b/src/fmacros.h
@@ -46,6 +46,10 @@
 #define _XOPEN_SOURCE
 #endif
 
+#if defined(__sun)
+#define _POSIX_C_SOURCE 199506L
+#endif
+
 #define _LARGEFILE_SOURCE
 #define _FILE_OFFSET_BITS 64