diff --git a/mysql-test/r/func_set.result b/mysql-test/r/func_set.result
index f9374d246d3..a860ce57cb4 100644
--- a/mysql-test/r/func_set.result
+++ b/mysql-test/r/func_set.result
@@ -316,3 +316,10 @@ invalid column     0       bravo,delta,foxtrot
 invalid column         0       foxtrot
 invalid column         0       alpha
 DROP TABLE t1;
+#
+# Bug#119995 FIND_IN_SET() returns wrong result
+#
+SET collation_connection = 'utf8mb4_0900_ai_ci';
+SELECT FIND_IN_SET('ắ', 'a');
+FIND_IN_SET('ắ', 'a')
+1
diff --git a/mysql-test/t/func_set.test b/mysql-test/t/func_set.test
index 1416a1f7fd2..8f0d5986eb1 100644
--- a/mysql-test/t/func_set.test
+++ b/mysql-test/t/func_set.test
@@ -205,3 +205,10 @@ UNION
 SELECT 'invalid column  ', FIND_IN_SET(z, s), s FROM t1;

 DROP TABLE t1;
+
+--echo #
+--echo # Bug#119995 FIND_IN_SET() returns wrong result
+--echo #
+
+SET collation_connection = 'utf8mb4_0900_ai_ci';
+SELECT FIND_IN_SET('ắ', 'a');
diff --git a/sql/item_func.cc b/sql/item_func.cc
index bf9823a24ed..dfd2a934d04 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -4570,7 +4570,7 @@ longlong Item_func_find_in_set::val_int() {
   String *buffer = args[1]->val_str(&value2);
   if (buffer == nullptr) return error_int();

-  if (buffer->length() >= find->length()) {
+  if (buffer->numchars() >= find->numchars()) {
     my_wc_t wc = 0;
     const CHARSET_INFO *cs = cmp_collation.collation;
     const char *str_begin = buffer->ptr();