diff --git a/src/proto/textprop.pro b/src/proto/textprop.pro
index aa06e61..4b9a7a4 100644
--- a/src/proto/textprop.pro
+++ b/src/proto/textprop.pro
@@ -10,6 +10,7 @@
 int find_visible_prop(win_T *wp, int type_id, int id, textprop_T *prop, linenr_T *found_lnum);
 void add_text_props(linenr_T lnum, textprop_T *text_props, int text_prop_count);
 proptype_T *text_prop_type_by_id(buf_T *buf, int id);
+int text_prop_type_valid(buf_T *buf, textprop_T *prop);
 void f_prop_clear(typval_T *argvars, typval_T *rettv);
 void f_prop_find(typval_T *argvars, typval_T *rettv);
 void f_prop_list(typval_T *argvars, typval_T *rettv);