diff --git a/mysql-test/r/ctype_utf8.result b/mysql-test/r/ctype_utf8.result
index 217d3ca26d8..121168c2a2a 100644
--- a/mysql-test/r/ctype_utf8.result
+++ b/mysql-test/r/ctype_utf8.result
@@ -5830,5 +5830,44 @@ OCTET_LENGTH(a)	a
 255	ＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡ
 DROP TABLE t1;
 #
+# MDEV-8402 Bug#77473 Bug#21317406 TRUNCATED DATA WITH SUBQUERY & UTF8
+#
+#
+SET NAMES utf8;
+SELECT length(rpad(_utf8 0xD0B1, 65536, _utf8 0xD0B2)) AS data;
+data
+131072
+SELECT length(data) AS len FROM (
+SELECT rpad(_utf8 0xD0B1, 65536, _utf8 0xD0B2) AS data
+) AS sub;
+len
+131072
+SELECT length(rpad(_utf8 0xD0B1, 65535, _utf8 0xD0B2)) AS data;
+data
+131070
+SELECT length(data) AS len FROM (
+SELECT rpad(_utf8 0xD0B1, 65535, _utf8 0xD0B2) AS data
+) AS sub;
+len
+131070
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 36766) AS data) AS sub;
+len
+73532
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 36767) AS data) AS sub;
+len
+73534
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 36778) AS data) AS sub;
+len
+73556
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 65535) AS data) AS sub;
+len
+131070
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 65536) AS data) AS sub;
+len
+131072
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 65537) AS data) AS sub;
+len
+131074
+#
 # End of 5.5 tests
 #
diff --git a/mysql-test/r/ctype_utf8mb4.result b/mysql-test/r/ctype_utf8mb4.result
index 448645ebbae..17a1a2f787e 100644
--- a/mysql-test/r/ctype_utf8mb4.result
+++ b/mysql-test/r/ctype_utf8mb4.result
@@ -2622,6 +2622,40 @@ OCTET_LENGTH(a)	a
 252	😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎
 DROP TABLE t1;
 #
+# MDEV-8402 Bug#77473 Bug#21317406 TRUNCATED DATA WITH SUBQUERY & UTF8
+#
+#
+SET NAMES utf8mb4;
+SELECT length(repeat(_utf8mb4 0xE29883, 21844)) AS data;
+data
+65532
+SELECT length(data) AS len
+FROM ( SELECT repeat(_utf8mb4 0xE29883, 21844) AS data ) AS sub;
+len
+65532
+SELECT length(repeat(_utf8mb4 0xE29883, 21846)) AS data;
+data
+65538
+SELECT length(data) AS len
+FROM ( SELECT repeat(_utf8mb4 0xE29883, 21846) AS data ) AS sub;
+len
+65538
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 21844) AS data ) AS sub;
+len
+65532
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 21845) AS data ) AS sub;
+len
+65535
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 21846) AS data ) AS sub;
+len
+65538
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 65535) AS data ) AS sub;
+len
+196605
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 65536) AS data ) AS sub;
+len
+196608
+#
 # End of 5.5 tests
 #
 #
diff --git a/mysql-test/t/ctype_utf8.test b/mysql-test/t/ctype_utf8.test
index a9b5cee11ce..d6fdc6c6a2c 100644
--- a/mysql-test/t/ctype_utf8.test
+++ b/mysql-test/t/ctype_utf8.test
@@ -1658,6 +1658,29 @@ ALTER TABLE t1 MODIFY a TINYTEXT CHARACTER SET utf8;
 SELECT OCTET_LENGTH(a),a FROM t1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-8402 Bug#77473 Bug#21317406 TRUNCATED DATA WITH SUBQUERY & UTF8
+--echo #
+--echo #
+
+SET NAMES utf8;
+SELECT length(rpad(_utf8 0xD0B1, 65536, _utf8 0xD0B2)) AS data;
+SELECT length(data) AS len FROM (
+  SELECT rpad(_utf8 0xD0B1, 65536, _utf8 0xD0B2) AS data
+) AS sub;
+
+SELECT length(rpad(_utf8 0xD0B1, 65535, _utf8 0xD0B2)) AS data;
+SELECT length(data) AS len FROM (
+  SELECT rpad(_utf8 0xD0B1, 65535, _utf8 0xD0B2) AS data
+) AS sub;
+
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 36766) AS data) AS sub;
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 36767) AS data) AS sub;
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 36778) AS data) AS sub;
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 65535) AS data) AS sub;
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 65536) AS data) AS sub;
+SELECT length(data) AS len FROM (SELECT REPEAT('ä', 65537) AS data) AS sub;
+
 --echo #
 --echo # End of 5.5 tests
 --echo #
diff --git a/mysql-test/t/ctype_utf8mb4.test b/mysql-test/t/ctype_utf8mb4.test
index 66f5a3ba5ac..c240f261af4 100644
--- a/mysql-test/t/ctype_utf8mb4.test
+++ b/mysql-test/t/ctype_utf8mb4.test
@@ -1838,6 +1838,26 @@ SELECT OCTET_LENGTH(a),a FROM t1;
 DROP TABLE t1;
 
 
+--echo #
+--echo # MDEV-8402 Bug#77473 Bug#21317406 TRUNCATED DATA WITH SUBQUERY & UTF8
+--echo #
+--echo #
+
+SET NAMES utf8mb4;
+SELECT length(repeat(_utf8mb4 0xE29883, 21844)) AS data;
+SELECT length(data) AS len
+FROM ( SELECT repeat(_utf8mb4 0xE29883, 21844) AS data ) AS sub;
+
+SELECT length(repeat(_utf8mb4 0xE29883, 21846)) AS data;
+SELECT length(data) AS len
+FROM ( SELECT repeat(_utf8mb4 0xE29883, 21846) AS data ) AS sub;
+
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 21844) AS data ) AS sub;
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 21845) AS data ) AS sub;
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 21846) AS data ) AS sub;
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 65535) AS data ) AS sub;
+SELECT LENGTH(data) AS len FROM (SELECT REPEAT('☃', 65536) AS data ) AS sub;
+
 --echo #
 --echo # End of 5.5 tests
 --echo #
diff --git a/sql/field.h b/sql/field.h
index fdf229edfbb..f8fc7427618 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1854,10 +1854,9 @@ public:
     packlength= 4;
     if (set_packlength)
     {
-      uint32 l_char_length= len_arg/cs->mbmaxlen;
-      packlength= l_char_length <= 255 ? 1 :
-                  l_char_length <= 65535 ? 2 :
-                  l_char_length <= 16777215 ? 3 : 4;
+      packlength= len_arg <= 255 ? 1 :
+                  len_arg <= 65535 ? 2 :
+                  len_arg <= 16777215 ? 3 : 4;
     }
   }
   Field_blob(uint32 packlength_arg)