diff --git a/gtk/encodesymbolic.c b/gtk/encodesymbolic.c
index 6f4ba57a41..c8e6700501 100644
--- a/gtk/encodesymbolic.c
+++ b/gtk/encodesymbolic.c
@@ -30,6 +30,7 @@
 #endif
 #include <errno.h>
 #include <stdlib.h>
+#include <locale.h>
 
 static gchar *output_dir = NULL;