diff --git a/mysql-test/suite/engines/funcs/r/in_text_boundary_error.result b/mysql-test/suite/engines/funcs/r/in_text_boundary_error.result
new file mode 100644
index 00000000000..43f4b36254b
--- /dev/null
+++ b/mysql-test/suite/engines/funcs/r/in_text_boundary_error.result
@@ -0,0 +1,12 @@
+SET SQL_MODE="TRADITIONAL,ANSI";
+DROP TABLE IF EXISTS t1;
+CREATE TABLE t1(c1 TINYTEXT CHARACTER SET utf8mb4);
+INSERT INTO t1 (c1) VALUES(REPEAT('A', 255));
+INSERT INTO t1 (c1) VALUES(REPEAT('A', 256));
+ERROR 22001: Data too long for column 'c1' at row 1
+INSERT INTO t1 (c1) VALUES(REPEAT(X'C385', 127));
+INSERT INTO t1 (c1) VALUES(REPEAT(X'C385', 128));
+ERROR 22001: Data too long for column 'c1' at row 1
+INSERT INTO t1 (c1) VALUES(CONCAT('a', REPEAT(X'C385', 128)));
+ERROR 22001: Data too long for column 'c1' at row 1
+DROP TABLE t1;
diff --git a/mysql-test/suite/engines/funcs/t/in_text_boundary_error.test b/mysql-test/suite/engines/funcs/t/in_text_boundary_error.test
new file mode 100644
index 00000000000..f7f582283b3
--- /dev/null
+++ b/mysql-test/suite/engines/funcs/t/in_text_boundary_error.test
@@ -0,0 +1,14 @@
+SET SQL_MODE="TRADITIONAL,ANSI";
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+--enable_warnings
+CREATE TABLE t1(c1 TINYTEXT CHARACTER SET utf8mb4);
+INSERT INTO t1 (c1) VALUES(REPEAT('A', 255));
+--error 1406
+INSERT INTO t1 (c1) VALUES(REPEAT('A', 256));
+INSERT INTO t1 (c1) VALUES(REPEAT(X'C385', 127));
+--error 1406
+INSERT INTO t1 (c1) VALUES(REPEAT(X'C385', 128));
+--error 1406
+INSERT INTO t1 (c1) VALUES(CONCAT('a', REPEAT(X'C385', 128)));
+DROP TABLE t1;
diff --git a/sql-common/sql_string.cc b/sql-common/sql_string.cc
index aa93e684f1e..f64daf88cbc 100644
--- a/sql-common/sql_string.cc
+++ b/sql-common/sql_string.cc
@@ -1008,6 +1008,7 @@ size_t well_formed_copy_nchars(const CHARSET_INFO *to_cs,
     {
       int well_formed_error;
       uint from_offset;
+      size_t min_length;
 
       if ((from_offset= (from_length % to_cs->mbminlen)) &&
           (from_cs == &my_charset_bin))
@@ -1045,13 +1046,25 @@ size_t well_formed_copy_nchars(const CHARSET_INFO *to_cs,
         to_length-= to_cs->mbminlen;
       }
 
-      set_if_smaller(from_length, to_length);
-      res= to_cs->cset->well_formed_len(to_cs, from, from + from_length,
+      min_length = min(from_length, to_length);
+      res= to_cs->cset->well_formed_len(to_cs,
+                                        from, from + min_length,
                                         nchars, &well_formed_error);
       if (res > 0)
         memmove(to, from, res);
       *from_end_pos= from + res;
-      *well_formed_error_pos= well_formed_error ? from + res : NULL;
+      if (well_formed_error &&
+          (min_length - res < to_cs->mbmaxlen))
+      {
+        const char *from_end= from + min(res + to_cs->mbmaxlen, from_length);
+        size_t extra;
+
+        extra= to_cs->cset->well_formed_len(to_cs,
+                                            *from_end_pos, from_end,
+                                            1, &well_formed_error);
+        well_formed_error= extra >= 1 ? 0 : 1;
+      }
+      *well_formed_error_pos= well_formed_error ? *from_end_pos : NULL;
       *cannot_convert_error_pos= NULL;
       if (from_offset)
         res+= to_cs->mbminlen;