diff --git a/src/proto/testing.pro b/src/proto/testing.pro
index 3e203f8..0d4ff49 100644
--- a/src/proto/testing.pro
+++ b/src/proto/testing.pro
@@ -36,4 +36,5 @@
 void f_test_setmouse(typval_T *argvars, typval_T *rettv);
 void f_test_gui_mouse_event(typval_T *argvars, typval_T *rettv);
 void f_test_settime(typval_T *argvars, typval_T *rettv);
+void f_test_gui_drop_files(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */