diff --git a/app/models/submission.rb b/app/models/submission.rb
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -10,6 +10,11 @@
   validates_presence_of :source
   validates_length_of :source, :maximum => 100_000, :allow_blank => true, :message => 'too long'
   validates_length_of :source, :minimum => 1, :allow_blank => true, :message => 'too short'
+
+  validates_presence_of :output
+  validates_length_of :output, :maximum => 100_000, :allow_blank => true, :message => 'too long'
+  validates_length_of :output, :minimum => 1, :allow_blank => true, :message => 'too short'
+
   validate :must_have_valid_problem
   validate :must_specify_language