diff --git a/lib/schema.php b/lib/schema.php
index c32e6b5230..20bd95f28a 100644
--- a/lib/schema.php
+++ b/lib/schema.php
@@ -142,6 +142,7 @@ class Schema
      */
     public function buildCreateTable($name, $def)
     {
+        $def = $this->validateDef($name, $def);
         $def = $this->filterDef($def);
         $sql = array();
 
@@ -517,7 +518,7 @@ class Schema
      * @return array of SQL statements
      */
 
-    function buildEnsureTable($tableName, $def)
+    function buildEnsureTable($tableName, array $def)
     {
         try {
             $old = $this->getTableDef($tableName);
@@ -527,6 +528,7 @@ class Schema
 
         // Filter the DB-independent table definition to match the current
         // database engine's features and limitations.
+        $def = $this->validateDef($tableName, $def);
         $def = $this->filterDef($def);
 
         $statements = array();
@@ -851,10 +853,10 @@ class Schema
      * with plugins written for 0.9.x.
      *
      * @param string $tableName
-     * @param array $defs
+     * @param array $defs: array of ColumnDef objects
      * @return array
      */
-    function oldToNew($tableName, $defs)
+    protected function oldToNew($tableName, array $defs)
     {
         $table = array();
         $prefixes = array(
@@ -864,7 +866,6 @@ class Schema
             'big',
         );
         foreach ($defs as $cd) {
-            $cd->addToTableDef($table);
             $column = array();
             $column['type'] = $cd->type;
             foreach ($prefixes as $prefix) {
@@ -928,6 +929,31 @@ class Schema
         return $tableDef;
     }
 
+    /**
+     * Validate a table definition array, checking for basic structure.
+     *
+     * If necessary, converts from an old-style array of ColumnDef objects.
+     *
+     * @param string $tableName
+     * @param array $def: table definition array
+     * @return array validated table definition array
+     *
+     * @throws Exception on wildly invalid input
+     */
+    function validateDef($tableName, array $def)
+    {
+        if (count($defs) && $defs[0] instanceof ColumnDef) {
+            $def = $this->oldToNew($tableName, $defs);
+        }
+
+        // A few quick checks :D
+        if (!isset($def['fields'])) {
+            throw new Exceptioni("Invalid table definition for $tableName: no fields.");
+        }
+
+        return $def;
+    }
+
     function isNumericType($type)
     {
         $type = strtolower($type);
diff --git a/lib/schemaupdater.php b/lib/schemaupdater.php
new file mode 100644
index 0000000000..b872b0d578
--- /dev/null
+++ b/lib/schemaupdater.php
@@ -0,0 +1,117 @@
+<?php
+
+/**
+ * StatusNet, the distributed open-source microblogging tool
+ *
+ * Database schema utilities
+ *
+ * PHP version 5
+ *
+ * LICENCE: This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @category  Database
+ * @package   StatusNet
+ * @author    Evan Prodromou <evan@status.net>
+ * @copyright 2009 StatusNet, Inc.
+ * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
+ * @link      http://status.net/
+ */
+
+if (!defined('STATUSNET')) {
+    exit(1);
+}
+
+class SchemaUpdater
+{
+    public function __construct($schema)
+    {
+        $this->schema = $schema;
+        $this->conn = $conn;
+        $this->checksums = $this->getChecksums();
+    }
+
+    /**
+     * @param array $tableDefs
+     * @fixme handle tables that belong on different database servers...?
+     */
+    public function checkTables(array $tableDefs)
+    {
+        $checksums = $this->checksums;
+        foreach ($tableDefs as $table => $def) {
+            $checksum = $this->tableChecksum($def);
+            if (empty($checksums[$table])) {
+                common_log(LOG_DEBUG, "No previous schema_version for $table: updating to $checksum");
+            } else if ($checksums[$table] == $checksum) {
+                common_log(LOG_DEBUG, "Last schema_version for $table up to date: $checksum");
+                continue;
+            } else {
+                common_log(LOG_DEBUG, "Last schema_version for $table is {$checksums[$table]}: updating to $checksum");
+            }
+            $this->conn->query('BEGIN');
+            $this->schema->ensureTable($table, $def);
+            $this->saveChecksum($table, $checksum);
+            $this->conn->commit();
+        }
+    }
+
+    /**
+     * Calculate a checksum for this table definition array.
+     *
+     * @param array $def
+     * @return string
+     */
+    public function checksum(array $def)
+    {
+        $flat = serialize($def);
+        return sha1($flat);
+    }
+
+    /**
+     * Pull all known table checksums into an array for easy lookup.
+     *
+     * @return array: associative array of table names to checksum strings
+     */
+    protected function getChecksums()
+    {
+        $checksums = array();
+
+        $sv = new Schema_version();
+        $sv->find();
+        while ($sv->fetch()) {
+            $checksums[$sv->table_name] = $sv->checksum;
+        }
+
+        return $checksums;
+    }
+
+    /**
+     * Save or update current available checksums.
+     *
+     * @param string $table
+     * @param string $checksum
+     */
+    protected function saveChecksum($table, $checksum)
+    {
+        $sv = new Schema_version();
+        $sv->table_name = $table;
+        $sv->checksum = $checksum;
+        $sv->modified = common_sql_now();
+        if (isset($this->checksums[$table])) {
+            $sv->update();
+        } else {
+            $sv->insert();
+        }
+        $this->checksums[$table] = $checksum;
+    }
+}
diff --git a/scripts/dumpschema.php b/scripts/dumpschema.php
index 613364487a..2b238f0066 100644
--- a/scripts/dumpschema.php
+++ b/scripts/dumpschema.php
@@ -28,11 +28,12 @@ Attempt to pull a schema definition for a given table.
   --raw     skip compatibility filtering for diffs
   --create  dump SQL that would be run to update or create this table
   --build   dump SQL that would be run to create this table fresh
+  --checksum just output checksums from the source schema defs
 
 
 END_OF_CHECKSCHEMA_HELP;
 
-$longoptions = array('diff', 'all', 'create', 'update', 'raw');
+$longoptions = array('diff', 'all', 'create', 'update', 'raw', 'checksum');
 require_once INSTALLDIR.'/scripts/commandline.inc';
 
 function indentOptions($indent)
@@ -207,6 +208,24 @@ function tweakPrimaryKey($def)
     return $def;
 }
 
+function dumpChecksum($tableName)
+{
+    $schema = Schema::get();
+    $def = getCoreSchema($tableName);
+
+    $updater = new SchemaUpdater($schema);
+    $checksum = $updater->checksum($def);
+    $old = @$updater->checksums[$tableName];
+
+    if ($old == $checksum) {
+        echo "OK  $checksum $tableName\n";
+    } else if (!$old) {
+        echo "NEW $checksum $tableName\n";
+    } else {
+        echo "MOD $checksum $tableName (was $old)\n";
+    }
+}
+
 if (have_option('all')) {
     $args = getCoreTables();
 }
@@ -219,6 +238,8 @@ if (count($args)) {
             dumpBuildTable($tableName);
         } else if (have_option('update')) {
             dumpEnsureTable($tableName);
+        } else if (have_option('checksum')) {
+            dumpChecksum($tableName);
         } else {
             dumpTable($tableName, true);
         }