diff --git a/src/evalfunc.c b/src/evalfunc.c
index b4e4220..2a82812 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -5874,7 +5874,7 @@
 	int	utf8 = 0;
 
 	if (argvars[1].v_type != VAR_UNKNOWN)
-	    utf8 = (int)tv_get_number_chk(&argvars[1], NULL);
+	    utf8 = (int)tv_get_bool_chk(&argvars[1], NULL);
 	if (utf8)
 	    buf[utf_char2bytes((int)tv_get_number(&argvars[0]), buf)] = NUL;
 	else