diff --git a/lib/jekyll/convertible.rb b/lib/jekyll/convertible.rb
index e710b6f0..11d5fa86 100644
--- a/lib/jekyll/convertible.rb
+++ b/lib/jekyll/convertible.rb
@@ -69,7 +69,7 @@ module Jekyll
     end
 
     def validate_permalink!(filename)
-      if self.data["permalink"] && self.data["permalink"].empty?
+      if self.data["permalink"] && self.data["permalink"].to_s.empty?
         raise Errors::InvalidPermalinkError, "Invalid permalink in #{filename}"
       end
     end