diff --git a/mysql-test/r/ctype_utf8.result b/mysql-test/r/ctype_utf8.result
index c57b06f4895..fee561941f0 100644
--- a/mysql-test/r/ctype_utf8.result
+++ b/mysql-test/r/ctype_utf8.result
@@ -1167,3 +1167,11 @@ set @a:=null;
 execute my_stmt using @a;
 a	b
 drop table if exists t1;
+CREATE TABLE t1 (t TINYTEXT CHARACTER SET utf8);
+INSERT INTO t1 VALUES(REPEAT('a', 100));
+CREATE TEMPORARY TABLE t2 SELECT COALESCE(t) AS bug FROM t1;
+SELECT LENGTH(bug) FROM t2;
+LENGTH(bug)
+100
+DROP TABLE t2;
+DROP TABLE t1;
diff --git a/mysql-test/t/ctype_utf8.test b/mysql-test/t/ctype_utf8.test
index a96564f4e76..c9b2b9fc18f 100644
--- a/mysql-test/t/ctype_utf8.test
+++ b/mysql-test/t/ctype_utf8.test
@@ -868,6 +868,16 @@ set names utf8;
 select distinct char(a) from t1;
 drop table t1;
 
+#
+# Bug#15581: COALESCE function truncates mutli-byte TINYTEXT values
+#
+CREATE TABLE t1 (t TINYTEXT CHARACTER SET utf8);
+INSERT INTO t1 VALUES(REPEAT('a', 100));
+CREATE TEMPORARY TABLE t2 SELECT COALESCE(t) AS bug FROM t1;
+SELECT LENGTH(bug) FROM t2;
+DROP TABLE t2;
+DROP TABLE t1;
+
 # End of 4.1 tests
 
 #
diff --git a/sql/field.cc b/sql/field.cc
index 1f3649e1b88..d72c4913d99 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -8981,11 +8981,11 @@ uint32 Field_blob::max_length()
   switch (packlength)
   {
   case 1:
-    return 255;
+    return 255 * field_charset->mbmaxlen;
   case 2:
-    return 65535;
+    return 65535 * field_charset->mbmaxlen;
   case 3:
-    return 16777215;
+    return 16777215 * field_charset->mbmaxlen;
   case 4:
     return (uint32) 4294967295U;
   default: