Index: lib/redmine/wiki_formatting/textile/redcloth3.rb
===================================================================
--- lib/redmine/wiki_formatting/textile/redcloth3.rb	(revision 17596)
+++ lib/redmine/wiki_formatting/textile/redcloth3.rb	(working copy)
@@ -1034,7 +1034,7 @@
     def flush_left( text )
         indt = 0
         if text =~ /^ /
-            while text !~ /^ {#{indt}}\S/
+            while text !~ /^ {#{indt}}[^ ]/
                 indt += 1
             end unless text.empty?
             if indt.nonzero?
Index: test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb
===================================================================
--- test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb	(revision 17596)
+++ test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb	(working copy)
@@ -599,6 +599,12 @@
     assert_equal expected.gsub(%r{[\r\n\t]}, ''), to_html(text).gsub(%r{[\r\n\t]}, '')
   end
 
+  # TODO: Remove this test after migrating to RedCloth 4
+  def test_should_not_crash_with_special_input
+    assert_nothing_raised { to_html(" \f") }
+    assert_nothing_raised { to_html(" \v") }
+  end
+
   private
 
   def assert_html_output(to_test, expect_paragraph = true)