--- ext/mbstring/libmbfl/filters/mbfilter_utf8_mobile.c.bak	2019-01-09 10:54:13.000000000 +0100
+++ ext/mbstring/libmbfl/filters/mbfilter_utf8_mobile.c	2026-03-03 18:51:24.912344206 +0100
@@ -36,6 +36,8 @@
 #include "mbfilter_utf8_mobile.h"
 #include "mbfilter_sjis_mobile.h"
 
+int mbfl_filt_put_invalid_char(int c, mbfl_convert_filter *filter);
+
 extern int mbfl_filt_ident_utf8(int c, mbfl_identify_filter *filter);
 extern int mbfl_filt_conv_utf8_wchar_flush(mbfl_convert_filter *filter);