Index: trac/db/mysql_backend.py
===================================================================
--- trac/db/mysql_backend.py	(revision 7477)
+++ trac/db/mysql_backend.py	(working copy)
@@ -128,6 +128,8 @@
                 # Override the column type, as a text field cannot
                 # use auto_increment.
                 column.type = 'int'
+            if column.type == 'text':
+                ctype = 'varchar(255)'
             coldefs.append('    `%s` %s' % (column.name, ctype))
         if len(table.key) > 0:
             coldefs.append('    PRIMARY KEY (%s)' %