diff --git a/libratbox/configure b/libratbox/configure
index af408af..ab3c1ed 100755
--- a/libratbox/configure
+++ b/libratbox/configure
@@ -21357,7 +21357,8 @@ fi
      CPPFLAGS="$CFLAGS -D_ALL_SOURCE -D_XOPEN_SOURCE=500"
      ;;
 *solaris*)
-     CPPFLAGS="$CFLAGS -D_POSIX_PTHREAD_SEMANTICS"
+*sunos*)
+     CPPFLAGS="$CFLAGS -D_POSIX_PTHREAD_SEMANTICS -D_XPG4_2 -D__EXTENSIONS__"
      ;;
 *)
      ;;