diff --git a/phpBB/phpbb/plupload/plupload.php b/phpBB/phpbb/plupload/plupload.php
index 9ad12b1082..5a5b8a1874 100644
--- a/phpBB/phpbb/plupload/plupload.php
+++ b/phpBB/phpbb/plupload/plupload.php
@@ -274,22 +274,37 @@ class plupload
 	}
 
 	/**
-	* Checks various php.ini values and the maximum file size to determine
-	* the maximum size chunks a file can be split up into for upload
-	*
-	* @return int
-	*/
+	 * Checks various php.ini values to determine the maximum chunk
+	 * size a file should be split into for upload.
+	 *
+	 * The intention is to calculate a value which reflects whatever
+	 * the most restrictive limit is set to.  And to then set the chunk
+	 * size to half that value, to ensure any required transfer overhead
+	 * and POST data remains well within the limit.  Or, if all of the
+	 * limits are set to unlimited, the chunk size will also be unlimited.
+	 *
+	 * @return int
+	 *
+	 * @access public
+	 */
 	public function get_chunk_size()
 	{
-		$max = min(
+		$max = 0;
+
+		$limits = [
+			$this->php_ini->getBytes('memory_limit'),
 			$this->php_ini->getBytes('upload_max_filesize'),
 			$this->php_ini->getBytes('post_max_size'),
-			max(1, $this->php_ini->getBytes('memory_limit')),
-			$this->config['max_filesize']
-		);
+		];
+
+		foreach ($limits as $limit_type)
+		{
+			if ($limit_type > 0)
+			{
+				$max = ($max !== 0) ? min($limit_type, $max) : $limit_type;
+			}
+		}
 
-		// Use half of the maximum possible to leave plenty of room for other
-		// POST data.
 		return floor($max / 2);
 	}
 
diff --git a/tests/plupload/plupload_test.php b/tests/plupload/plupload_test.php
index 46bebb8d35..eb4657afbc 100644
--- a/tests/plupload/plupload_test.php
+++ b/tests/plupload/plupload_test.php
@@ -54,4 +54,77 @@ class phpbb_plupload_test extends phpbb_test_case
 
 		$this->assertEquals($expected, $plupload->generate_resize_string());
 	}
+
+	public function data_get_chunk_size()
+	{
+		return [
+			[[
+				'memory_limit' => -1,
+				'upload_max_filesize' => 0,
+				'post_max_size' => 0,
+			], 0],
+			[[
+				'memory_limit' => -1,
+				'upload_max_filesize' => 500,
+				'post_max_size' => 400,
+			], 200],
+			[[
+				'memory_limit' => 100,
+				'upload_max_filesize' => 0,
+				'post_max_size' => 300,
+			], 50],
+			[[
+				'memory_limit' => 300,
+				'upload_max_filesize' => 200,
+				'post_max_size' => 0,
+			], 100],
+			[[
+				'memory_limit' => 3000,
+				'upload_max_filesize' => 800,
+				'post_max_size' => 900,
+			], 400],
+			[[
+				'memory_limit' => 2000,
+				'upload_max_filesize' => 1000,
+				'post_max_size' => 600,
+			], 300],
+			[[
+				'memory_limit' => 1000,
+				'upload_max_filesize' => 2000,
+				'post_max_size' => 3000,
+			], 500],
+		];
+	}
+
+	/**
+	 * @dataProvider data_get_chunk_size
+	 */
+	public function test_get_chunk_size($limits_ary, $expected)
+	{
+		global $phpbb_root_path, $phpEx;
+
+		$lang = new \phpbb\language\language(new \phpbb\language\language_file_loader($phpbb_root_path, $phpEx));
+		$config = new \phpbb\config\config([]);
+
+		$ini_wrapper = $this->getMockBuilder('\bantu\IniGetWrapper\IniGetWrapper')
+			->setMethods(['getBytes'])
+			->getMock();
+		$ini_wrapper->method('getBytes')
+			->will($this->returnValueMap([
+				['memory_limit', $limits_ary['memory_limit']],
+				['upload_max_filesize', $limits_ary['upload_max_filesize']],
+				['post_max_size', $limits_ary['post_max_size']]
+			]));
+
+		$plupload = new \phpbb\plupload\plupload(
+			'',
+			$config,
+			new phpbb_mock_request,
+			new \phpbb\user($lang, '\phpbb\datetime'),
+			$ini_wrapper,
+			new \phpbb\mimetype\guesser(array(new \phpbb\mimetype\extension_guesser))
+		);
+
+		$this->assertEquals($expected, $plupload->get_chunk_size());
+	}
 }