diff --git a/phpBB/includes/captcha/captcha_gd.php b/phpBB/includes/captcha/captcha_gd.php
index 5f24618aab..ecdad43978 100644
--- a/phpBB/includes/captcha/captcha_gd.php
+++ b/phpBB/includes/captcha/captcha_gd.php
@@ -77,7 +77,7 @@ class captcha
 		{
 			$denom = ($code_len - $i);
 			$denom = max(1.3, $denom);
-			$offset[$i] = mt_rand(0, (1.5 * $width_avail) / $denom);
+			$offset[$i] = phpbb_mt_rand(0, (int) round((1.5 * $width_avail) / $denom));
 			$width_avail -= $offset[$i];
 		}
 
diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 2d9d2c225f..c48eb6d102 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -249,6 +249,22 @@ function unique_id($extra = 'c')
 	return substr($val, 4, 16);
 }
 
+/**
+* Wrapper for mt_rand() which allows swapping $min and $max parameters.
+*
+* PHP does not allow us to swap the order of the arguments for mt_rand() anymore.
+* (since PHP 5.3.4, see http://bugs.php.net/46587)
+*
+* @param int $min		Lowest value to be returned
+* @param int $max		Highest value to be returned
+*
+* @return int			Random integer between $min and $max (or $max and $min)
+*/
+function phpbb_mt_rand($min, $max)
+{
+	return ($min > $max) ? mt_rand($max, $min) : mt_rand($min, $max);
+}
+
 /**
 * Return formatted string for filesizes
 *
diff --git a/tests/random/mt_rand.php b/tests/random/mt_rand.php
new file mode 100644
index 0000000000..d6502c4e80
--- /dev/null
+++ b/tests/random/mt_rand.php
@@ -0,0 +1,46 @@
+<?php
+/**
+*
+* @package testing
+* @copyright (c) 2011 phpBB Group
+* @license http://opensource.org/licenses/gpl-license.php GNU Public License
+*
+*/
+
+require_once dirname(__FILE__) . '/../../phpBB/includes/functions.php';
+
+class phpbb_random_mt_rand_test extends phpbb_test_case
+{
+	public function test_max_equals_min()
+	{
+		$result = phpbb_mt_rand(42, 42);
+		$this->assertEquals(42, $result);
+	}
+
+	public function test_max_equals_min_negative()
+	{
+		$result = phpbb_mt_rand(-42, -42);
+		$this->assertEquals(-42, $result);
+	}
+
+	public function test_max_greater_min()
+	{
+		$result = phpbb_mt_rand(3, 4);
+		$this->assertGreaterThanOrEqual(3, $result);
+		$this->assertLessThanOrEqual(4, $result);
+	}
+
+	public function test_min_greater_max()
+	{
+		$result = phpbb_mt_rand(4, 3);
+		$this->assertGreaterThanOrEqual(3, $result);
+		$this->assertLessThanOrEqual(4, $result);
+	}
+
+	public function test_min_greater_max_negative()
+	{
+		$result = phpbb_mt_rand(-3, -4);
+		$this->assertGreaterThanOrEqual(-4, $result);
+		$this->assertLessThanOrEqual(-3, $result);
+	}
+}