diff --git a/configure.ac b/configure.ac
index c5ab295468..c4d757c0fa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11,7 +11,7 @@
 m4_define([gtk_major_version], [3])
 m4_define([gtk_minor_version], [8])
 m4_define([gtk_micro_version], [8])
-m4_define([gtk_interface_age], [8])
+m4_define([gtk_interface_age], [9])
 m4_define([gtk_binary_age],
           [m4_eval(100 * gtk_minor_version + gtk_micro_version)])
 m4_define([gtk_version],