diff --git a/system/database/drivers/odbc/odbc_result.php b/system/database/drivers/odbc/odbc_result.php
index bfd6949..572e110 100644
--- a/system/database/drivers/odbc/odbc_result.php
+++ b/system/database/drivers/odbc/odbc_result.php
@@ -38,15 +38,27 @@
  */
 class CI_DB_odbc_result extends CI_DB_result {
 
+	public $num_rows;
+
 	/**
 	 * Number of rows in the result set
 	 *
-	 * @access	public
-	 * @return	integer
+	 * @return	int
 	 */
-	function num_rows()
+	public function num_rows()
 	{
-		return @odbc_num_rows($this->result_id);
+		if (is_int($this->num_rows))
+		{
+			return $this->num_rows;
+		}
+
+		// Work-around for ODBC subdrivers that don't support num_rows()
+		if (($this->num_rows = @odbc_num_rows($this->result_id)) === -1)
+		{
+			$this->num_rows = count($this->result_array());
+		}
+
+		return $this->num_rows;
 	}
 
 	// --------------------------------------------------------------------
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index bd9776c..d43291d 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -114,6 +114,7 @@
 -  Fixed a bug (#177) - CI_Form_validation::set_value() didn't set the default value if POST data is NULL.
 -  Fixed a bug (#68, #414) - Oracle's escape_str() didn't properly escape LIKE wild characters.
 -  Fixed a bug (#81) - ODBC's list_fields() and field_data() methods skipped the first column due to odbc_field_*() functions' index starting at 1 instead of 0.
+-  Fixed a bug (#129) - ODBC's num_rows() returned -1 in some cases, due to not all subdrivers supporting the odbc_num_rows() function.
 
 Version 2.1.1
 =============