diff --git a/src/proto/vim9compile.pro b/src/proto/vim9compile.pro
index 67c7224..0f3ebc3 100644
--- a/src/proto/vim9compile.pro
+++ b/src/proto/vim9compile.pro
@@ -10,6 +10,7 @@
 int assignment_len(char_u *p, int *heredoc);
 int check_vim9_unlet(char_u *name);
 int compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx);
+void set_function_type(ufunc_T *ufunc);
 void delete_instr(isn_T *isn);
 void delete_def_function(ufunc_T *ufunc);
 void free_def_functions(void);