diff --git a/middleman-core/lib/middleman-core/contracts.rb b/middleman-core/lib/middleman-core/contracts.rb
index a61952e5..ed3fcf97 100644
--- a/middleman-core/lib/middleman-core/contracts.rb
+++ b/middleman-core/lib/middleman-core/contracts.rb
@@ -23,7 +23,7 @@ if ENV['TEST'] || ENV['CONTRACTS'] == 'true'
       end
 
       def valid?(val)
-        (val.frozen? || val.nil?) && Contract.valid?(val, @contract)
+        (val.frozen? || val.nil? || [::TrueClass, ::FalseClass, ::Fixnum].include?(val.class)) && Contract.valid?(val, @contract)
       end
     end