diff --git a/mysql-test/r/ctype_utf8.result b/mysql-test/r/ctype_utf8.result
index 03d3ab9f22e..cf9426e6b21 100644
--- a/mysql-test/r/ctype_utf8.result
+++ b/mysql-test/r/ctype_utf8.result
@@ -1070,3 +1070,11 @@ char(a)
 1
 2
 drop table 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 8c0e03c0cd3..01bffe9492e 100644
--- a/mysql-test/t/ctype_utf8.test
+++ b/mysql-test/t/ctype_utf8.test
@@ -882,4 +882,14 @@ 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 abb5297f458..b1d9167aee2 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -6949,11 +6949,11 @@ 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: