diff --git a/libs/tk/ytk/wscript b/libs/tk/ytk/wscript
index 11721244d1..63e1c2afc5 100644
--- a/libs/tk/ytk/wscript
+++ b/libs/tk/ytk/wscript
@@ -282,7 +282,7 @@ def build(bld):
     obj.uselib          = 'GLIB GIO PANGO CAIRO PANGOCAIRO GMODULE'
     obj.defines         = [ 'HAVE_CONFIG_H', '_LARGEFILE64_SOURCE', '_REENTRANT', 'G_LOG_DOMAIN="Gtk"', 'GTK_COMPILATION', '_FILE_OFFSET_BITS=64', 'GTK_DISABLE_DEPRECATED', 'G_DISABLE_CAST_CHECKS',
                             'G_DISABLE_SINGLE_INCLUDES', 'DATK_DISABLE_SINGLE_INCLUDES', 'GDK_PIXBUF_DISABLE_SINGLE_INCLUDES', 'GTK_DISABLE_SINGLE_INCLUDES', 'GDK_PIXBUF_DISABLE_DEPRECATED',
-                            'GTK_PRINT_BACKENDS="file,lpr"', 'GTK_PRINT_BACKEND_ENABLE_UNSUPPORTED', 'GTK_PRINT_PREVIEW_COMMAND=""',
+                            'GTK_PRINT_BACKENDS="file,lpr"', 'GTK_PRINT_BACKEND_ENABLE_UNSUPPORTED', 'GTK_PRINT_PREVIEW_COMMAND=""', '_POSIX_C_SOURCE=200809L',
                             'GTK_VERSION="2.24.23"', 'GTK_BINARY_VERSION="2.10.0"', 'GTK_HOST="ardour"',
                             'PACKAGE="' + I18N_PACKAGE + '"',
                             'GETTEXT_PACKAGE="' + I18N_PACKAGE + '"',