diff --git a/mysql-test/include/ctype_filesort2.inc b/mysql-test/include/ctype_filesort2.inc
index 7b09eb482a5..7b576034136 100644
--- a/mysql-test/include/ctype_filesort2.inc
+++ b/mysql-test/include/ctype_filesort2.inc
@@ -14,3 +14,12 @@ SELECT HEX(a), HEX(CONVERT(a USING utf8mb4)) FROM t1 ORDER BY a;
 ALTER TABLE t1 ADD KEY(a);
 SELECT HEX(a), HEX(CONVERT(a USING utf8mb4)) FROM t1 ORDER BY a;
 DROP TABLE IF EXISTS t1;
+--echo #
+--echo # BUG#16691598 - ORDER BY LOWER(COLUMN) PRODUCES
+--echo #                OUT-OF-ORDER RESULTS
+--echo #
+CREATE TABLE  t1 SELECT ('a a') as n;
+INSERT INTO t1 VALUES('a b');
+SELECT * FROM t1 ORDER BY LOWER(n) ASC;
+SELECT * FROM t1 ORDER BY LOWER(n) DESC;
+DROP TABLE t1;
diff --git a/mysql-test/r/ctype_utf16.result b/mysql-test/r/ctype_utf16.result
index 42897ca580f..70b1ddde5c7 100644
--- a/mysql-test/r/ctype_utf16.result
+++ b/mysql-test/r/ctype_utf16.result
@@ -636,6 +636,21 @@ FF9D	EFBE9D
 D800DF84	F0908E84
 DBC0DC00	F4808080
 DROP TABLE IF EXISTS t1;
+#
+# BUG#16691598 - ORDER BY LOWER(COLUMN) PRODUCES
+#                OUT-OF-ORDER RESULTS
+#
+CREATE TABLE  t1 SELECT ('a a') as n;
+INSERT INTO t1 VALUES('a b');
+SELECT * FROM t1 ORDER BY LOWER(n) ASC;
+n
+a a
+a b
+SELECT * FROM t1 ORDER BY LOWER(n) DESC;
+n
+a b
+a a
+DROP TABLE t1;
 select @@collation_connection;
 @@collation_connection
 utf16_bin
diff --git a/mysql-test/r/ctype_utf32.result b/mysql-test/r/ctype_utf32.result
index 2433f2426a4..85e6220f5e8 100644
--- a/mysql-test/r/ctype_utf32.result
+++ b/mysql-test/r/ctype_utf32.result
@@ -635,6 +635,21 @@ HEX(a)	HEX(CONVERT(a USING utf8mb4))
 00010384	F0908E84
 00100000	F4808080
 DROP TABLE IF EXISTS t1;
+#
+# BUG#16691598 - ORDER BY LOWER(COLUMN) PRODUCES
+#                OUT-OF-ORDER RESULTS
+#
+CREATE TABLE  t1 SELECT ('a a') as n;
+INSERT INTO t1 VALUES('a b');
+SELECT * FROM t1 ORDER BY LOWER(n) ASC;
+n
+a a
+a b
+SELECT * FROM t1 ORDER BY LOWER(n) DESC;
+n
+a b
+a a
+DROP TABLE t1;
 select @@collation_connection;
 @@collation_connection
 utf32_bin
diff --git a/mysql-test/r/ctype_utf8mb4.result b/mysql-test/r/ctype_utf8mb4.result
index c7084134cd3..fa5abc5425f 100644
--- a/mysql-test/r/ctype_utf8mb4.result
+++ b/mysql-test/r/ctype_utf8mb4.result
@@ -1012,6 +1012,21 @@ EFBE9D	EFBE9D
 F0908E84	F0908E84
 F4808080	F4808080
 DROP TABLE IF EXISTS t1;
+#
+# BUG#16691598 - ORDER BY LOWER(COLUMN) PRODUCES
+#                OUT-OF-ORDER RESULTS
+#
+CREATE TABLE  t1 SELECT ('a a') as n;
+INSERT INTO t1 VALUES('a b');
+SELECT * FROM t1 ORDER BY LOWER(n) ASC;
+n
+a a
+a b
+SELECT * FROM t1 ORDER BY LOWER(n) DESC;
+n
+a b
+a a
+DROP TABLE t1;
 select @@collation_connection;
 @@collation_connection
 utf8mb4_bin
diff --git a/sql/filesort.cc b/sql/filesort.cc
index 6f59c505615..20a290d24a0 100644
--- a/sql/filesort.cc
+++ b/sql/filesort.cc
@@ -813,8 +813,6 @@ static void make_sortkey(register SORTPARAM *param,
       {
         CHARSET_INFO *cs=item->collation.collation;
         char fill_char= ((cs->state & MY_CS_BINSORT) ? (char) 0 : ' ');
-        int diff;
-        uint sort_field_length;
 
         if (maybe_null)
           *to++=1;
@@ -842,25 +840,13 @@ static void make_sortkey(register SORTPARAM *param,
           break;
         }
         length= res->length();
-        sort_field_length= sort_field->length - sort_field->suffix_length;
-        diff=(int) (sort_field_length - length);
-        if (diff < 0)
-        {
-          diff=0;
-          length= sort_field_length;
-        }
-        if (sort_field->suffix_length)
-        {
-          /* Store length last in result_string */
-          store_length(to + sort_field_length, length,
-                       sort_field->suffix_length);
-        }
         if (sort_field->need_strxnfrm)
         {
           char *from=(char*) res->ptr();
           uint tmp_length;
           if ((uchar*) from == to)
           {
+            DBUG_ASSERT(sort_field->length >= length);
             set_if_smaller(length,sort_field->length);
             memcpy(param->tmp_buffer,from,length);
             from=param->tmp_buffer;
@@ -871,6 +857,22 @@ static void make_sortkey(register SORTPARAM *param,
         }
         else
         {
+          uint diff;
+          uint sort_field_length= sort_field->length -
+            sort_field->suffix_length;
+          if (sort_field_length < length)
+          {
+            diff= 0;
+            length= sort_field_length;
+          }
+          else
+            diff= sort_field_length - length;
+          if (sort_field->suffix_length)
+          {
+            /* Store length last in result_string */
+            store_length(to + sort_field_length, length,
+                         sort_field->suffix_length);
+          }
           my_strnxfrm(cs,(uchar*)to,length,(const uchar*)res->ptr(),length);
           cs->cset->fill(cs, (char *)to+length,diff,fill_char);
         }
diff --git a/strings/ctype-ucs2.c b/strings/ctype-ucs2.c
index cecd4424108..f1d0e775804 100644
--- a/strings/ctype-ucs2.c
+++ b/strings/ctype-ucs2.c
@@ -1664,7 +1664,7 @@ CHARSET_INFO my_charset_utf16_general_ci=
 CHARSET_INFO my_charset_utf16_bin=
 {
   55,0,0,              /* number       */
-  MY_CS_COMPILED|MY_CS_BINSORT|MY_CS_UNICODE|MY_CS_NONASCII,
+  MY_CS_COMPILED|MY_CS_BINSORT|MY_CS_STRNXFRM|MY_CS_UNICODE|MY_CS_NONASCII,
   "utf16",             /* cs name      */
   "utf16_bin",         /* name         */
   "UTF-16 Unicode",    /* comment      */
diff --git a/strings/ctype-utf8.c b/strings/ctype-utf8.c
index 4976a9cf31a..62d5fbe0111 100644
--- a/strings/ctype-utf8.c
+++ b/strings/ctype-utf8.c
@@ -5435,7 +5435,8 @@ CHARSET_INFO my_charset_utf8mb4_general_ci=
 CHARSET_INFO my_charset_utf8mb4_bin=
 {
   46,0,0,             /* number       */
-  MY_CS_COMPILED|MY_CS_BINSORT|MY_CS_UNICODE|MY_CS_UNICODE_SUPPLEMENT, /* state  */
+  MY_CS_COMPILED|MY_CS_BINSORT|MY_CS_STRNXFRM|MY_CS_UNICODE|
+  MY_CS_UNICODE_SUPPLEMENT, /* state  */
   MY_UTF8MB4,         /* cs name      */
   MY_UTF8MB4_BIN,     /* name         */
   "UTF-8 Unicode",    /* comment      */