diff --git a/dibi/drivers/firebird.php b/dibi/drivers/firebird.php
index 8a0bd214..69a18dae 100644
--- a/dibi/drivers/firebird.php
+++ b/dibi/drivers/firebird.php
@@ -373,7 +373,7 @@ class DibiFirebirdDriver extends DibiObject implements IDibiDriver, IDibiResultD
 	 */
 	public function getRowCount()
 	{
-		return ibase_num_fields($this->resultSet);
+		throw new DibiNotSupportedException("Firebird/Interbase do not support returning number of rows in result set.");
 	}