diff --git includes/database/pgsql/schema.inc includes/database/pgsql/schema.inc
index e2a6a27..e7c393d 100644
--- includes/database/pgsql/schema.inc
+++ includes/database/pgsql/schema.inc
@@ -471,16 +471,28 @@ class DatabaseSchema_pgsql extends DatabaseSchema {
       $typecast = 'int';
     }
 
+    $this->connection->query('ALTER TABLE {' . $table . '} ALTER "' . $field . '" TYPE ' . $typecast . ' USING "' . $field . '"::' . $typecast);
 
-    $this->connection->query("ALTER TABLE {" . $table . "} ALTER $field SET $field_new = CAST(" . $field . "_old as " . $typecast . ")");
-
-    $this->addField($table, "$field_new", $spec);
-
-    $this->dropField($table, $field . '_old');
+    // Type "serial" is known to postgres, but *only* during table creation, not
+    // when altering. Because of that, the sequence needs to be created and
+    // initialized by hand.
+    if (in_array($map[$spec['type'] . ':' . $spec['size']], array('serial', 'bigserial'))) {
+      $seq = "{" . $table . "}_" . $field_new . "_seq";
+      $this->connection->query("CREATE SEQUENCE " . $seq);
+      // Set sequence to maximal field value to not conflict with existing
+      // entries.
+      $this->connection->query("SELECT setval('" . $seq . "', MAX(" . $field . ")) FROM {" . $table . "}");
+      $this->connection->query('ALTER TABLE {' . $table . '} ALTER "' . $field . '" SET DEFAULT nextval(\'' . $seq . '\')');
+    }
 
     // Rename the column if necessary.
     if ($field != $field_new) {
-      $this->connection->query('ALTER TABLE {' . $table . '} RENAME "' . $field . '" TO "' . $field_new . '_old"');
+      $this->connection->query('ALTER TABLE {' . $table . '} RENAME "' . $field . '" TO "' . $field_new . '"');
+    }
+
+    // Change description if necessary.
+    if (!empty($spec['description'])) {
+      $this->connection->query('COMMENT ON COLUMN {' . $table . '}.' . $field_new . ' IS ' . $this->prepareComment($spec['description']));
     }
 
     if (isset($new_keys)) {