diff --git a/src/Dibi/Drivers/Sqlite3Driver.php b/src/Dibi/Drivers/Sqlite3Driver.php
index 98e80aae..bf0fa9b5 100644
--- a/src/Dibi/Drivers/Sqlite3Driver.php
+++ b/src/Dibi/Drivers/Sqlite3Driver.php
@@ -450,7 +450,7 @@ class Sqlite3Driver implements Dibi\Driver, Dibi\ResultDriver
 	 * @param  int     num of arguments
 	 * @return void
 	 */
-	public function registerFunction($name, $callback, $numArgs = -1)
+	public function registerFunction($name, callable $callback, $numArgs = -1)
 	{
 		$this->connection->createFunction($name, $callback, $numArgs);
 	}
@@ -464,7 +464,7 @@ class Sqlite3Driver implements Dibi\Driver, Dibi\ResultDriver
 	 * @param  int     num of arguments
 	 * @return void
 	 */
-	public function registerAggregateFunction($name, $rowCallback, $agrCallback, $numArgs = -1)
+	public function registerAggregateFunction($name, callable $rowCallback, callable $agrCallback, $numArgs = -1)
 	{
 		$this->connection->createAggregate($name, $rowCallback, $agrCallback, $numArgs);
 	}
diff --git a/src/Dibi/HashMap.php b/src/Dibi/HashMap.php
index 63218f10..e33bc5c6 100644
--- a/src/Dibi/HashMap.php
+++ b/src/Dibi/HashMap.php
@@ -17,18 +17,14 @@ abstract class HashMapBase
 	private $callback;
 
 
-	public function __construct($callback)
+	public function __construct(callable $callback)
 	{
-		$this->setCallback($callback);
+		$this->callback = $callback;
 	}
 
 
-	public function setCallback($callback)
+	public function setCallback(callable $callback)
 	{
-		if (!is_callable($callback)) {
-			$able = is_callable($callback, TRUE, $textual);
-			throw new \InvalidArgumentException("Handler '$textual' is not " . ($able ? 'callable.' : 'valid PHP callback.'));
-		}
 		$this->callback = $callback;
 	}
 
diff --git a/src/Dibi/Result.php b/src/Dibi/Result.php
index 2fb2849c..2ddab6c6 100644
--- a/src/Dibi/Result.php
+++ b/src/Dibi/Result.php
@@ -172,10 +172,9 @@ class Result implements IDataSource
 
 	/**
 	 * Set a factory to create fetched object instances. These should extend the Row class.
-	 * @param  callback
 	 * @return self
 	 */
-	public function setRowFactory($callback)
+	public function setRowFactory(callable $callback)
 	{
 		$this->rowFactory = $callback;
 		return $this;