diff --git a/mysql-test/r/fulltext.result b/mysql-test/r/fulltext.result
index 9c69f7fd88e..806675edc5a 100644
--- a/mysql-test/r/fulltext.result
+++ b/mysql-test/r/fulltext.result
@@ -631,4 +631,17 @@ CREATE TABLE t1(a CHAR(1),FULLTEXT(a));
 SELECT 1 FROM t1 WHERE MATCH(a) AGAINST ('') AND ROW(a,a) > ROW(1,1);
 1
 DROP TABLE t1;
+#
+# BUG#51866 - crash with repair by sort and fulltext keys
+#
+CREATE TABLE t1(a CHAR(4), FULLTEXT(a));
+INSERT INTO t1 VALUES('aaaa');
+SET myisam_sort_buffer_size=4;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '4'
+REPAIR TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	repair	status	OK
+SET myisam_sort_buffer_size=@@global.myisam_sort_buffer_size;
+DROP TABLE t1;
 End of 5.1 tests
diff --git a/mysql-test/r/gis-rtree.result b/mysql-test/r/gis-rtree.result
index 58c603673df..eb9c350f589 100644
--- a/mysql-test/r/gis-rtree.result
+++ b/mysql-test/r/gis-rtree.result
@@ -1540,5 +1540,12 @@ a
 HANDLER t1 READ a LAST;
 a
 HANDLER t1 CLOSE;
+HANDLER t1 OPEN;
+HANDLER t1 READ a FIRST;
+a
+INSERT INTO t1 VALUES (GeomFromText('Polygon((40 40,60 40,60 60,40 60,40 40))'));
+# should not crash
+HANDLER t1 READ a NEXT;
+HANDLER t1 CLOSE;
 DROP TABLE t1;
 End of 5.0 tests.
diff --git a/mysql-test/r/handler_myisam.result b/mysql-test/r/handler_myisam.result
index 90a1bdfe6be..a970e20a2c0 100644
--- a/mysql-test/r/handler_myisam.result
+++ b/mysql-test/r/handler_myisam.result
@@ -756,4 +756,17 @@ TRUNCATE t1;
 HANDLER t1 READ FIRST;
 ERROR 42S02: Unknown table 't1' in HANDLER
 DROP TABLE t1;
+#
+# BUG#51877 - HANDLER interface causes invalid memory read
+#
+CREATE TABLE t1(a INT, KEY(a));
+HANDLER t1 OPEN;
+HANDLER t1 READ a FIRST;
+a
+INSERT INTO t1 VALUES(1);
+HANDLER t1 READ a NEXT;
+a
+1
+HANDLER t1 CLOSE;
+DROP TABLE t1;
 End of 5.1 tests
diff --git a/mysql-test/r/myisam.result b/mysql-test/r/myisam.result
index 5b9745a7b81..433fc7c16a7 100644
--- a/mysql-test/r/myisam.result
+++ b/mysql-test/r/myisam.result
@@ -2313,6 +2313,8 @@ INSERT INTO t1 SELECT a+1280,b FROM t1;
 INSERT INTO t1 SELECT a+2560,b FROM t1;
 INSERT INTO t1 SELECT a+5120,b FROM t1;
 SET myisam_sort_buffer_size=4;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '4'
 REPAIR TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	repair	error	myisam_sort_buffer_size is too small
@@ -2363,6 +2365,8 @@ CREATE TABLE t1(a CHAR(255), KEY(a));
 SELECT * FROM t1, t1 AS a1;
 a	a
 SET myisam_sort_buffer_size=4;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '4'
 INSERT INTO t1 VALUES
 ('0'),('0'),('0'),('0'),('0'),('0'),('0'),('0'),('0'),('0'),
 ('0'),('0'),('0'),('0'),('0'),('0'),('0'),('0'),('0'),('0'),
diff --git a/mysql-test/r/variables.result b/mysql-test/r/variables.result
index 7f45046fab5..ff6d4cf85d9 100644
--- a/mysql-test/r/variables.result
+++ b/mysql-test/r/variables.result
@@ -523,6 +523,8 @@ select @@max_user_connections;
 100
 set global max_write_lock_count=100;
 set myisam_sort_buffer_size=100;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '100'
 set global net_buffer_length=100;
 Warnings:
 Warning	1292	Truncated incorrect net_buffer_length value: '100'
diff --git a/mysql-test/suite/sys_vars/r/myisam_sort_buffer_size_basic_32.result b/mysql-test/suite/sys_vars/r/myisam_sort_buffer_size_basic_32.result
index 2657d599df7..cdc73b99316 100644
--- a/mysql-test/suite/sys_vars/r/myisam_sort_buffer_size_basic_32.result
+++ b/mysql-test/suite/sys_vars/r/myisam_sort_buffer_size_basic_32.result
@@ -8,11 +8,15 @@ SELECT @start_session_value;
 8388608
 '#--------------------FN_DYNVARS_005_01-------------------------#'
 SET @@global.myisam_sort_buffer_size   = 100;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '100'
 SET @@global.myisam_sort_buffer_size   = DEFAULT;
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
 8388608
 SET @@session.myisam_sort_buffer_size   = 200;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '200'
 SET @@session.myisam_sort_buffer_size   = DEFAULT;
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
@@ -28,9 +32,11 @@ SELECT @@session.myisam_sort_buffer_size   = 8388608;
 1
 '#--------------------FN_DYNVARS_005_03-------------------------#'
 SET @@global.myisam_sort_buffer_size   = 4;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '4'
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
-4
+4096
 SET @@global.myisam_sort_buffer_size   = 4294967295;
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
@@ -41,9 +47,11 @@ SELECT @@global.myisam_sort_buffer_size  ;
 655354
 '#--------------------FN_DYNVARS_005_04-------------------------#'
 SET @@session.myisam_sort_buffer_size   = 4;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '4'
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
-4
+4096
 SET @@session.myisam_sort_buffer_size   = 4294967295;
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
@@ -58,13 +66,13 @@ Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '0'
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
-4
+4096
 SET @@global.myisam_sort_buffer_size   = -1024;
 Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '-1024'
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
-4
+4096
 SET @@global.myisam_sort_buffer_size   = 429496729533;
 Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '429496729533'
@@ -101,28 +109,28 @@ Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '0'
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
-4
+4096
 SET @@session.myisam_sort_buffer_size   = -2;
 Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '-2'
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
-4
+4096
 SET @@session.myisam_sort_buffer_size   = 65530.34.;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.' at line 1
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
-4
+4096
 SET @@session.myisam_sort_buffer_size   = test;
 ERROR 42000: Incorrect argument type to variable 'myisam_sort_buffer_size'
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
-4
+4096
 SET @@session.myisam_sort_buffer_size   = "test";
 ERROR 42000: Incorrect argument type to variable 'myisam_sort_buffer_size'
 SELECT @@session.myisam_sort_buffer_size  ;
 @@session.myisam_sort_buffer_size
-4
+4096
 '#------------------FN_DYNVARS_005_06-----------------------#'
 SELECT @@global.myisam_sort_buffer_size   = VARIABLE_VALUE 
 FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES 
@@ -141,20 +149,24 @@ Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '1'
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
-4
+4096
 SET @@global.myisam_sort_buffer_size   = FALSE;
 Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '0'
 SELECT @@global.myisam_sort_buffer_size  ;
 @@global.myisam_sort_buffer_size
-4
+4096
 '#---------------------FN_DYNVARS_001_09----------------------#'
 SET @@global.myisam_sort_buffer_size   = 10;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '10'
 SELECT @@myisam_sort_buffer_size   = @@global.myisam_sort_buffer_size  ;
 @@myisam_sort_buffer_size   = @@global.myisam_sort_buffer_size
-0
+1
 '#---------------------FN_DYNVARS_001_10----------------------#'
 SET @@myisam_sort_buffer_size   = 100;
+Warnings:
+Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '100'
 SELECT @@myisam_sort_buffer_size   = @@local.myisam_sort_buffer_size  ;
 @@myisam_sort_buffer_size   = @@local.myisam_sort_buffer_size
 1
@@ -167,7 +179,7 @@ Warnings:
 Warning	1292	Truncated incorrect myisam_sort_buffer_size value: '1'
 SELECT @@myisam_sort_buffer_size  ;
 @@myisam_sort_buffer_size
-4
+4096
 SELECT local.myisam_sort_buffer_size  ;
 ERROR 42S02: Unknown table 'local' in field list
 SELECT session.myisam_sort_buffer_size  ;
diff --git a/mysql-test/t/fulltext.test b/mysql-test/t/fulltext.test
index afaabb781b8..ec64728a8c9 100644
--- a/mysql-test/t/fulltext.test
+++ b/mysql-test/t/fulltext.test
@@ -575,5 +575,14 @@ CREATE TABLE t1(a CHAR(1),FULLTEXT(a));
 SELECT 1 FROM t1 WHERE MATCH(a) AGAINST ('') AND ROW(a,a) > ROW(1,1);
 DROP TABLE t1;
 
+--echo #
+--echo # BUG#51866 - crash with repair by sort and fulltext keys
+--echo #
+CREATE TABLE t1(a CHAR(4), FULLTEXT(a));
+INSERT INTO t1 VALUES('aaaa');
+SET myisam_sort_buffer_size=4;
+REPAIR TABLE t1;
+SET myisam_sort_buffer_size=@@global.myisam_sort_buffer_size;
+DROP TABLE t1;
 
 --echo End of 5.1 tests
diff --git a/mysql-test/t/gis-rtree.test b/mysql-test/t/gis-rtree.test
index c5d5bfee861..b006096528e 100644
--- a/mysql-test/t/gis-rtree.test
+++ b/mysql-test/t/gis-rtree.test
@@ -914,14 +914,15 @@ HANDLER t1 READ a PREV;
 HANDLER t1 READ a LAST;
 HANDLER t1 CLOSE;
 
-#TODO: re-enable this test please when bug #51877 is solved
 # second crash fixed when the tree has changed since the last search.
-#HANDLER t1 OPEN;
-#HANDLER t1 READ a FIRST;
-#INSERT INTO t1 VALUES (GeomFromText('Polygon((40 40,60 40,60 60,40 60,40 40))'));
-#HANDLER t1 READ a NEXT;
-#HANDLER t1 CLOSE;
-#TODO: end of the 51877 dependent section
+HANDLER t1 OPEN;
+HANDLER t1 READ a FIRST;
+INSERT INTO t1 VALUES (GeomFromText('Polygon((40 40,60 40,60 60,40 60,40 40))'));
+--echo # should not crash
+--disable_result_log
+HANDLER t1 READ a NEXT;
+--enable_result_log
+HANDLER t1 CLOSE;
 
 DROP TABLE t1;
 
diff --git a/mysql-test/t/handler_myisam.test b/mysql-test/t/handler_myisam.test
index da02a90af0f..868ba14480a 100644
--- a/mysql-test/t/handler_myisam.test
+++ b/mysql-test/t/handler_myisam.test
@@ -37,4 +37,15 @@ TRUNCATE t1;
 HANDLER t1 READ FIRST;
 DROP TABLE t1;
 
+--echo #
+--echo # BUG#51877 - HANDLER interface causes invalid memory read
+--echo #
+CREATE TABLE t1(a INT, KEY(a));
+HANDLER t1 OPEN;
+HANDLER t1 READ a FIRST;
+INSERT INTO t1 VALUES(1);
+HANDLER t1 READ a NEXT;
+HANDLER t1 CLOSE;
+DROP TABLE t1;
+
 --echo End of 5.1 tests
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index f658a7c8c3c..bb685ba42e3 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -6858,7 +6858,7 @@ The minimum value for this variable is 4096.",
    "The buffer that is allocated when sorting the index when doing a REPAIR or when creating indexes with CREATE INDEX or ALTER TABLE.",
    (uchar**) &global_system_variables.myisam_sort_buff_size,
    (uchar**) &max_system_variables.myisam_sort_buff_size, 0,
-   GET_ULONG, REQUIRED_ARG, 8192*1024, 4, ~0L, 0, 1, 0},
+   GET_ULONG, REQUIRED_ARG, 8192 * 1024, 4096, ~0L, 0, 1, 0},
   {"myisam_use_mmap", OPT_MYISAM_USE_MMAP,
    "Use memory mapping for reading and writing MyISAM tables.",
    (uchar**) &opt_myisam_use_mmap,
diff --git a/storage/myisam/mi_check.c b/storage/myisam/mi_check.c
index c10cfdd0c9b..8e3864d1c44 100644
--- a/storage/myisam/mi_check.c
+++ b/storage/myisam/mi_check.c
@@ -2396,10 +2396,8 @@ int mi_repair_by_sort(MI_CHECK *param, register MI_INFO *info,
       /*
         fulltext indexes may have much more entries than the
         number of rows in the table. We estimate the number here.
-
-        Note, built-in parser is always nr. 0 - see ftparser_call_initializer()
       */
-      if (sort_param.keyinfo->ftkey_nr == 0)
+      if (sort_param.keyinfo->parser == &ft_default_parser)
       {
         /*
           for built-in parser the number of generated index entries
@@ -2416,8 +2414,9 @@ int mi_repair_by_sort(MI_CHECK *param, register MI_INFO *info,
           so, we'll use all the sort memory and start from ~10 buffpeks.
           (see _create_index_by_sort)
         */
-        sort_info.max_records=
-          10*param->sort_buffer_length/sort_param.key_length;
+        sort_info.max_records= 10 *
+                               max(param->sort_buffer_length, MIN_SORT_BUFFER) /
+                               sort_param.key_length;
       }
 
       sort_param.key_read=sort_ft_key_read;
diff --git a/storage/myisam/mi_open.c b/storage/myisam/mi_open.c
index e18146f2357..f2f390862bd 100644
--- a/storage/myisam/mi_open.c
+++ b/storage/myisam/mi_open.c
@@ -652,6 +652,9 @@ MI_INFO *mi_open(const char *name, int mode, uint open_flags)
   myisam_open_list=list_add(myisam_open_list,&m_info->open_list);
 
   pthread_mutex_unlock(&THR_LOCK_myisam);
+
+  bzero(info.buff, share->base.max_key_block_length * 2);
+
   if (myisam_log_file >= 0)
   {
     intern_filename(name_buff,share->index_file_name);
diff --git a/storage/myisam/mi_page.c b/storage/myisam/mi_page.c
index 23a2526f756..76fac8688a7 100644
--- a/storage/myisam/mi_page.c
+++ b/storage/myisam/mi_page.c
@@ -86,13 +86,6 @@ int _mi_write_keypage(register MI_INFO *info, register MI_KEYDEF *keyinfo,
   if ((length=keyinfo->block_length) > IO_SIZE*2 &&
       info->state->key_file_length != page+length)
     length= ((mi_getint(buff)+IO_SIZE-1) & (uint) ~(IO_SIZE-1));
-#ifdef HAVE_purify
-  {
-    length=mi_getint(buff);
-    bzero((uchar*) buff+length,keyinfo->block_length-length);
-    length=keyinfo->block_length;
-  }
-#endif
   DBUG_RETURN((key_cache_write(info->s->key_cache,
                          info->s->kfile,page, level, (uchar*) buff,length,
 			 (uint) keyinfo->block_length,
diff --git a/storage/myisam/mi_rnext.c b/storage/myisam/mi_rnext.c
index 7ce66d41e0f..b9bbda3cacb 100644
--- a/storage/myisam/mi_rnext.c
+++ b/storage/myisam/mi_rnext.c
@@ -28,6 +28,7 @@ int mi_rnext(MI_INFO *info, uchar *buf, int inx)
 {
   int error,changed;
   uint flag;
+  uint update_mask= HA_STATE_NEXT_FOUND;
   DBUG_ENTER("mi_rnext");
 
   if ((inx = _mi_check_index(info,inx)) < 0)
@@ -55,6 +56,20 @@ int mi_rnext(MI_INFO *info, uchar *buf, int inx)
 			   info->s->state.key_root[inx]);
       break;
     }
+    /*
+      "search first" failed. This means we have no pivot for
+      "search next", or in other words MI_INFO::lastkey is
+      likely uninitialized.
+
+      Normally SQL layer would never request "search next" if
+      "search first" failed. But HANDLER may do anything.
+
+      As mi_rnext() without preceeding mi_rkey()/mi_rfirst()
+      equals to mi_rfirst(), we must restore original state
+      as if failing mi_rfirst() was not called.
+    */
+    if (error)
+      update_mask|= HA_STATE_PREV_FOUND;
   }
   else
   {
@@ -100,7 +115,7 @@ int mi_rnext(MI_INFO *info, uchar *buf, int inx)
   }
 	/* Don't clear if database-changed */
   info->update&= (HA_STATE_CHANGED | HA_STATE_ROW_CHANGED);
-  info->update|= HA_STATE_NEXT_FOUND;
+  info->update|= update_mask;
 
   if (error)
   {
diff --git a/storage/myisam/mi_write.c b/storage/myisam/mi_write.c
index 624c31e57ff..72a4e006cc6 100644
--- a/storage/myisam/mi_write.c
+++ b/storage/myisam/mi_write.c
@@ -825,7 +825,7 @@ static int _mi_balance_page(register MI_INFO *info, MI_KEYDEF *keyinfo,
 	     (size_t) (length=new_left_length - left_length - k_length));
       pos=buff+2+length;
       memcpy((uchar*) father_key_pos,(uchar*) pos,(size_t) k_length);
-      bmove((uchar*) buff+2,(uchar*) pos+k_length,new_right_length);
+      bmove((uchar*) buff + 2, (uchar*) pos + k_length, new_right_length - 2);
     }
     else
     {						/* Move keys -> buff */
diff --git a/storage/myisam/rt_index.c b/storage/myisam/rt_index.c
index 31241a83228..410badd3145 100644
--- a/storage/myisam/rt_index.c
+++ b/storage/myisam/rt_index.c
@@ -641,18 +641,12 @@ static int rtree_insert_level(MI_INFO *info, uint keynr, uchar *key,
     }
     case 1: /* root was split, grow a new root */
     { 
-      uchar *new_root_buf;
+      uchar *new_root_buf= info->buff + info->s->base.max_key_block_length;
       my_off_t new_root;
       uchar *new_key;
       uint nod_flag = info->s->base.key_reflength;
 
       DBUG_PRINT("rtree", ("root was split, grow a new root"));
-      if (!(new_root_buf = (uchar*)my_alloca((uint)keyinfo->block_length + 
-                                             MI_MAX_KEY_BUFF)))
-      {
-        my_errno = HA_ERR_OUT_OF_MEM;
-        DBUG_RETURN(-1); /* purecov: inspected */
-      }
 
       mi_putint(new_root_buf, 2, nod_flag);
       if ((new_root = _mi_new(info, keyinfo, DFLT_INIT_HITS)) ==
@@ -680,10 +674,8 @@ static int rtree_insert_level(MI_INFO *info, uint keynr, uchar *key,
       DBUG_PRINT("rtree", ("new root page: %lu  level: %d  nod_flag: %u",
                            (ulong) new_root, 0, mi_test_if_nod(new_root_buf)));
 
-      my_afree((uchar*)new_root_buf);
       break;
 err1:
-      my_afree((uchar*)new_root_buf);
       DBUG_RETURN(-1); /* purecov: inspected */
     }
     default:
diff --git a/storage/myisam/rt_split.c b/storage/myisam/rt_split.c
index ef988dbd048..88cf643faf9 100644
--- a/storage/myisam/rt_split.c
+++ b/storage/myisam/rt_split.c
@@ -258,7 +258,7 @@ int rtree_split_page(MI_INFO *info, MI_KEYDEF *keyinfo, uchar *page, uchar *key,
   double *old_coord;
   int n_dim;
   uchar *source_cur, *cur1, *cur2;
-  uchar *new_page;
+  uchar *new_page= info->buff;
   int err_code= 0;
   uint nod_flag= mi_test_if_nod(page);
   uint full_length= key_length + (nod_flag ? nod_flag : 
@@ -304,12 +304,7 @@ int rtree_split_page(MI_INFO *info, MI_KEYDEF *keyinfo, uchar *page, uchar *key,
     goto split_err;
   }
 
-  if (!(new_page = (uchar*)my_alloca((uint)keyinfo->block_length)))
-  {
-    err_code= -1;
-    goto split_err;
-  }
-  
+  info->buff_used= 1;
   stop = task + (max_keys + 1);
   cur1 = rt_PAGE_FIRST_KEY(page, nod_flag);
   cur2 = rt_PAGE_FIRST_KEY(new_page, nod_flag);
@@ -345,8 +340,6 @@ int rtree_split_page(MI_INFO *info, MI_KEYDEF *keyinfo, uchar *page, uchar *key,
                                 DFLT_INIT_HITS, new_page);
   DBUG_PRINT("rtree", ("split new block: %lu", (ulong) *new_page_offs));
 
-  my_afree((uchar*)new_page);
-
 split_err:
   my_afree((uchar*) coord_buf);
   DBUG_RETURN(err_code);
diff --git a/storage/myisam/sort.c b/storage/myisam/sort.c
index e01dad68555..5dff1ea3558 100644
--- a/storage/myisam/sort.c
+++ b/storage/myisam/sort.c
@@ -28,13 +28,11 @@
 
 /* static variables */
 
-#undef MIN_SORT_MEMORY
 #undef MYF_RW
 #undef DISK_BUFFER_SIZE
 
 #define MERGEBUFF 15
 #define MERGEBUFF2 31
-#define MIN_SORT_MEMORY (4096-MALLOC_OVERHEAD)
 #define MYF_RW  MYF(MY_NABP | MY_WME | MY_WAIT_IF_FULL)
 #define DISK_BUFFER_SIZE (IO_SIZE*16)
 
@@ -131,12 +129,12 @@ int _create_index_by_sort(MI_SORT_PARAM *info,my_bool no_messages,
   sort_keys= (uchar **) NULL; error= 1;
   maxbuffer=1;
 
-  memavl=max(sortbuff_size,MIN_SORT_MEMORY);
+  memavl= max(sortbuff_size, MIN_SORT_BUFFER);
   records=	info->sort_info->max_records;
   sort_length=	info->key_length;
   LINT_INIT(keys);
 
-  while (memavl >= MIN_SORT_MEMORY)
+  while (memavl >= MIN_SORT_BUFFER)
   {
     if ((records < UINT_MAX32) && 
        ((my_off_t) (records + 1) * 
@@ -171,10 +169,10 @@ int _create_index_by_sort(MI_SORT_PARAM *info,my_bool no_messages,
 	break;
     }
     old_memavl=memavl;
-    if ((memavl=memavl/4*3) < MIN_SORT_MEMORY && old_memavl > MIN_SORT_MEMORY)
-      memavl=MIN_SORT_MEMORY;
+    if ((memavl= memavl/4*3) < MIN_SORT_BUFFER && old_memavl > MIN_SORT_BUFFER)
+      memavl= MIN_SORT_BUFFER;
   }
-  if (memavl < MIN_SORT_MEMORY)
+  if (memavl < MIN_SORT_BUFFER)
   {
     mi_check_print_error(info->sort_info->param,"MyISAM sort buffer too small"); /* purecov: tested */
     goto err; /* purecov: tested */
@@ -348,12 +346,12 @@ pthread_handler_t thr_find_all_keys(void *arg)
     bzero((char*) &sort_param->unique,  sizeof(sort_param->unique));
     sort_keys= (uchar **) NULL;
 
-    memavl=       max(sort_param->sortbuff_size, MIN_SORT_MEMORY);
+    memavl=       max(sort_param->sortbuff_size, MIN_SORT_BUFFER);
     idx=          (uint)sort_param->sort_info->max_records;
     sort_length=  sort_param->key_length;
     maxbuffer=    1;
 
-    while (memavl >= MIN_SORT_MEMORY)
+    while (memavl >= MIN_SORT_BUFFER)
     {
       if ((my_off_t) (idx+1)*(sort_length+sizeof(char*)) <=
           (my_off_t) memavl)
@@ -391,11 +389,11 @@ pthread_handler_t thr_find_all_keys(void *arg)
           break;
       }
       old_memavl= memavl;
-      if ((memavl= memavl/4*3) < MIN_SORT_MEMORY &&
-          old_memavl > MIN_SORT_MEMORY)
-        memavl= MIN_SORT_MEMORY;
+      if ((memavl= memavl / 4 * 3) < MIN_SORT_BUFFER &&
+          old_memavl > MIN_SORT_BUFFER)
+        memavl= MIN_SORT_BUFFER;
     }
-    if (memavl < MIN_SORT_MEMORY)
+    if (memavl < MIN_SORT_BUFFER)
     {
       mi_check_print_error(sort_param->sort_info->param,
                            "MyISAM sort buffer too small");
@@ -564,7 +562,7 @@ int thr_write_keys(MI_SORT_PARAM *sort_param)
       if (!mergebuf)
       {
         length=param->sort_buffer_length;
-        while (length >= MIN_SORT_MEMORY)
+        while (length >= MIN_SORT_BUFFER)
         {
           if ((mergebuf= my_malloc(length, MYF(0))))
               break;