diff --git a/app/models/wiki_file.rb b/app/models/wiki_file.rb
index 2c8caab5..b0b5b418 100644
--- a/app/models/wiki_file.rb
+++ b/app/models/wiki_file.rb
@@ -12,10 +12,9 @@ class WikiFile < ActiveRecord::Base
     first(:conditions => ['file_name = ?', file_name])
   end
 
-  SANE_FILE_NAME = /^[a-zA-Z0-9\-_\. ]*$/
   def validate
     if file_name 
-      if file_name !~ SANE_FILE_NAME
+      if ! is_valid?(file_name)
         errors.add("file_name", "is invalid. Only latin characters, digits, dots, underscores, " +
            "dashes and spaces are accepted")
       elsif file_name == '.' or file_name == '..'
@@ -58,7 +57,10 @@ class WikiFile < ActiveRecord::Base
     require 'fileutils'
     FileUtils.rm_f(content_path) if File.exists?(content_path)
   end
-  
-  
+
+  SANE_FILE_NAME = /^[a-zA-Z0-9\-_\. ]*$/  
+  def self.is_valid?(name)
+    name =~ SANE_FILE_NAME
+  end
   
 end
diff --git a/lib/url_generator.rb b/lib/url_generator.rb
index 22e6bd27..5d4a7dff 100644
--- a/lib/url_generator.rb
+++ b/lib/url_generator.rb
@@ -64,6 +64,7 @@ class UrlGenerator < AbstractUrlGenerator
   private
 
   def file_link(mode, name, text, web_address, known_file, description)
+    return bad_filename(name) unless WikiFile.is_valid?(name) 
     case mode
     when :export
       if known_file
@@ -116,6 +117,7 @@ class UrlGenerator < AbstractUrlGenerator
   end
 
   def pic_link(mode, name, text, web_address, known_pic)
+    return bad_filename(name) unless WikiFile.is_valid?(name) 
     href = @controller.url_for :controller => 'file', :web => web_address, :action => 'file',
       :id => name, :only_path => true
     case mode
@@ -141,6 +143,7 @@ class UrlGenerator < AbstractUrlGenerator
   end
 
   def media_link(mode, name, text, web_address, known_media, media_type)
+    return bad_filename(name) unless WikiFile.is_valid?(name) 
     href = @controller.url_for :controller => 'file', :web => web_address, :action => 'file',
       :id => name, :only_path => true
     case mode
@@ -177,6 +180,10 @@ class UrlGenerator < AbstractUrlGenerator
 
   private
 
+    def bad_filename(name)
+      "<span class='badWikiWord'>[[invalid filename: #{name}]]</span>"
+    end
+
     def wikilink_for(mode, name, text, web_address)
       web = Web.find_by_address(web_address)
       action = web.published? && (web != @web || [:publish, :s5].include?(mode) ) ? 'published' : 'show'
diff --git a/public/stylesheets/instiki.css b/public/stylesheets/instiki.css
index 1a6f72b4..d14510b3 100644
--- a/public/stylesheets/instiki.css
+++ b/public/stylesheets/instiki.css
@@ -100,6 +100,12 @@ border: 3px solid blue;
 padding: 2px;
 }
 
+.badWikiWord {
+background-color:#FCC;
+border: 1px solid blue;
+padding: 1px;
+}
+
 .deleteWikiWord:hover, .deleteWikiWord a:hover {
 background-color:#F88;
 }