diff --git a/lib/rdoc/rdoc.rb b/lib/rdoc/rdoc.rb
index 4d45d47978..f4bb58e14b 100644
--- a/lib/rdoc/rdoc.rb
+++ b/lib/rdoc/rdoc.rb
@@ -353,7 +353,11 @@ def parse_file filename
     return unless content
 
     filename_path = Pathname(filename).expand_path
-    relative_path = filename_path.relative_path_from @options.root
+    begin
+      relative_path = filename_path.relative_path_from @options.root
+    rescue ArgumentError
+      relative_path = filename_path
+    end
 
     if @options.page_dir and
        relative_path.to_s.start_with? @options.page_dir.to_s then