diff --git a/system/core/Common.php b/system/core/Common.php
index 85e18e4..d66649f 100644
--- a/system/core/Common.php
+++ b/system/core/Common.php
@@ -716,8 +716,8 @@
 		// carriage return (dec 13) and horizontal tab (dec 09)
 		if ($url_encoded)
 		{
-			$non_displayables[] = '/%0[0-8bcef]/';	// url encoded 00-08, 11, 12, 14, 15
-			$non_displayables[] = '/%1[0-9a-f]/';	// url encoded 16-31
+			$non_displayables[] = '/%0[0-8bcef]/i';	// url encoded 00-08, 11, 12, 14, 15
+			$non_displayables[] = '/%1[0-9a-f]/i';	// url encoded 16-31
 		}
 
 		$non_displayables[] = '/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]+/S';	// 00-08, 11, 12, 14-31, 127
diff --git a/tests/codeigniter/core/Common_test.php b/tests/codeigniter/core/Common_test.php
index 81a185e..ca19e5d 100644
--- a/tests/codeigniter/core/Common_test.php
+++ b/tests/codeigniter/core/Common_test.php
@@ -54,4 +54,16 @@
 		);
 	}
 
+	// ------------------------------------------------------------------------
+
+	public function test_remove_invisible_characters()
+	{
+		$raw_string = 'Here is a string containing invisible'.chr(0x08).' text %0e.';
+		$removed_string = 'Here is a string containing invisible text %0e.';
+		$this->assertEquals($removed_string, remove_invisible_characters($raw_string, FALSE));
+
+		$raw_string = 'Here is a string %0econtaining url_encoded invisible%1F text.';
+		$removed_string = 'Here is a string containing url_encoded invisible text.';
+		$this->assertEquals($removed_string, remove_invisible_characters($raw_string));
+	}
 }
\ No newline at end of file