diff --git a/lib/redmine/wiki_formatting/textile/redcloth3.rb b/lib/redmine/wiki_formatting/textile/redcloth3.rb
index 2ac134c0a..6d462e935 100644
--- a/lib/redmine/wiki_formatting/textile/redcloth3.rb
+++ b/lib/redmine/wiki_formatting/textile/redcloth3.rb
@@ -1034,7 +1034,7 @@ class RedCloth3 < String
     def flush_left( text )
         indt = 0
         if text =~ /^ /
-            while text !~ /^ {#{indt}}\S/
+            while text !~ /^ {#{indt}}[^ ]/
                 indt += 1
             end unless text.empty?
             if indt.nonzero?
diff --git a/test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb b/test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb
index 43ee83ce5..24098b782 100644
--- a/test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb
+++ b/test/unit/lib/redmine/wiki_formatting/textile_formatter_test.rb
@@ -580,6 +580,12 @@ STR
     }, false)
   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)