diff --git a/configure.ac b/configure.ac
index 0d72724d25..1a7a9109b9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -9,9 +9,9 @@
 # set GTK_BINARY_AGE and GTK_INTERFACE_AGE to 0.
 
 m4_define([gtk_major_version], [3])
-m4_define([gtk_minor_version], [20])
-m4_define([gtk_micro_version], [1])
-m4_define([gtk_interface_age], [1])
+m4_define([gtk_minor_version], [21])
+m4_define([gtk_micro_version], [0])
+m4_define([gtk_interface_age], [0])
 m4_define([gtk_binary_age],
           [m4_eval(100 * gtk_minor_version + gtk_micro_version)])
 m4_define([gtk_version],