diff --git a/libratbox/configure b/libratbox/configure
index ab3c1ed53..c0875e3bc 100755
--- a/libratbox/configure
+++ b/libratbox/configure
@@ -21356,8 +21356,7 @@ fi
 *interix*)
      CPPFLAGS="$CFLAGS -D_ALL_SOURCE -D_XOPEN_SOURCE=500"
      ;;
-*solaris*)
-*sunos*)
+*solaris*|*sunos*)
      CPPFLAGS="$CFLAGS -D_POSIX_PTHREAD_SEMANTICS -D_XPG4_2 -D__EXTENSIONS__"
      ;;
 *)