diff --git a/mysql-test/r/alter_table.result b/mysql-test/r/alter_table.result
index d8de2655c6c..82c35ff963a 100644
--- a/mysql-test/r/alter_table.result
+++ b/mysql-test/r/alter_table.result
@@ -826,3 +826,37 @@ create table t1 (t varchar(255) default null, key t (t(80)))
 engine=myisam default charset=latin1;
 alter table t1 change t t text;
 drop table t1;
+CREATE TABLE t1 (a varchar(500));
+ALTER TABLE t1 ADD b GEOMETRY NOT NULL, ADD SPATIAL INDEX(b);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` varchar(500) default NULL,
+  `b` geometry NOT NULL,
+  SPATIAL KEY `b` (`b`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+ALTER TABLE t1 ADD KEY(b(50));
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` varchar(500) default NULL,
+  `b` geometry NOT NULL,
+  SPATIAL KEY `b` (`b`),
+  KEY `b_2` (`b`(50))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+ALTER TABLE t1 ADD c POINT;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` varchar(500) default NULL,
+  `b` geometry NOT NULL,
+  `c` point default NULL,
+  SPATIAL KEY `b` (`b`),
+  KEY `b_2` (`b`(50))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+CREATE TABLE t2 (a INT, KEY (a(20)));
+ERROR HY000: Incorrect sub part key; the used key part isn't a string, the used length is longer than the key part, or the storage engine doesn't support unique sub keys
+ALTER TABLE t1 ADD d INT;
+ALTER TABLE t1 ADD KEY (d(20));
+ERROR HY000: Incorrect sub part key; the used key part isn't a string, the used length is longer than the key part, or the storage engine doesn't support unique sub keys
+DROP TABLE t1;
diff --git a/mysql-test/r/gis-rtree.result b/mysql-test/r/gis-rtree.result
index 05d0d5634e6..4ca2bc98d82 100644
--- a/mysql-test/r/gis-rtree.result
+++ b/mysql-test/r/gis-rtree.result
@@ -10,7 +10,7 @@ t1	CREATE TABLE `t1` (
   `fid` int(11) NOT NULL auto_increment,
   `g` geometry NOT NULL,
   PRIMARY KEY  (`fid`),
-  SPATIAL KEY `g` (`g`(32))
+  SPATIAL KEY `g` (`g`)
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 INSERT INTO t1 (g) VALUES (GeomFromText('LineString(150 150, 150 150)'));
 INSERT INTO t1 (g) VALUES (GeomFromText('LineString(149 149, 151 151)'));
@@ -293,7 +293,7 @@ t2	CREATE TABLE `t2` (
   `fid` int(11) NOT NULL auto_increment,
   `g` geometry NOT NULL,
   PRIMARY KEY  (`fid`),
-  SPATIAL KEY `g` (`g`(32))
+  SPATIAL KEY `g` (`g`)
 ) ENGINE=MyISAM AUTO_INCREMENT=101 DEFAULT CHARSET=latin1
 SELECT count(*) FROM t2;
 count(*)
diff --git a/mysql-test/t/alter_table.test b/mysql-test/t/alter_table.test
index 01f55931ca4..307138added 100644
--- a/mysql-test/t/alter_table.test
+++ b/mysql-test/t/alter_table.test
@@ -613,3 +613,26 @@ create table t1 (t varchar(255) default null, key t (t(80)))
 engine=myisam default charset=latin1;
 alter table t1 change t t text;
 drop table t1;
+
+#
+# Bug #26794: Adding an index with a prefix on a SPATIAL type breaks ALTER
+# TABLE
+#
+CREATE TABLE t1 (a varchar(500));
+
+ALTER TABLE t1 ADD b GEOMETRY NOT NULL, ADD SPATIAL INDEX(b);
+SHOW CREATE TABLE t1;
+ALTER TABLE t1 ADD KEY(b(50));
+SHOW CREATE TABLE t1;
+
+ALTER TABLE t1 ADD c POINT;
+SHOW CREATE TABLE t1;
+
+--error ER_WRONG_SUB_KEY
+CREATE TABLE t2 (a INT, KEY (a(20)));
+
+ALTER TABLE t1 ADD d INT;
+--error ER_WRONG_SUB_KEY
+ALTER TABLE t1 ADD KEY (d(20));
+
+DROP TABLE t1;
diff --git a/sql/field.cc b/sql/field.cc
index 981a877783f..0f8103b4046 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -1011,6 +1011,7 @@ bool Field::type_can_have_key_part(enum enum_field_types type)
   case MYSQL_TYPE_BLOB:
   case MYSQL_TYPE_VAR_STRING:
   case MYSQL_TYPE_STRING:
+  case MYSQL_TYPE_GEOMETRY:
     return TRUE;
   default:
     return FALSE;
diff --git a/sql/sql_show.cc b/sql/sql_show.cc
index c4b06934fc3..24aef80626f 100644
--- a/sql/sql_show.cc
+++ b/sql/sql_show.cc
@@ -992,7 +992,7 @@ store_create_info(THD *thd, TABLE_LIST *table_list, String *packet)
       if (key_part->field &&
           (key_part->length !=
            table->field[key_part->fieldnr-1]->key_length() &&
-           !(key_info->flags & HA_FULLTEXT)))
+           !(key_info->flags & (HA_FULLTEXT | HA_SPATIAL))))
       {
         buff[0] = '(';
         char* end=int10_to_str((long) key_part->length /
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 512d990347f..38a22c47f12 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -1344,6 +1344,7 @@ static int mysql_prepare_table(THD *thd, HA_CREATE_INFO *create_info,
 	}
 	else if (!f_is_geom(sql_field->pack_flag) &&
 		  (column->length > length ||
+                   !Field::type_can_have_key_part (sql_field->sql_type) ||
 		   ((f_is_packed(sql_field->pack_flag) ||
 		     ((file->table_flags() & HA_NO_PREFIX_CHAR_KEYS) &&
 		      (key_info->flags & HA_NOSAME))) &&
@@ -3470,7 +3471,8 @@ view_err:
           checking whether cfield->length < key_part_length (in chars).
          */
         if (!Field::type_can_have_key_part(cfield->field->type()) ||
-            !Field::type_can_have_key_part(cfield->sql_type) ||
+            (!Field::type_can_have_key_part(cfield->sql_type) &&
+             !f_is_geom (cfield->pack_flag)) ||
             (cfield->field->field_length == key_part_length &&
              !f_is_blob(key_part->key_type)) ||
 	    (cfield->length && (cfield->length < key_part_length /