diff --git a/lib/rdoc/task.rb b/lib/rdoc/task.rb
index 979c36254d..eaf5b36b49 100644
--- a/lib/rdoc/task.rb
+++ b/lib/rdoc/task.rb
@@ -244,6 +244,8 @@ def define
 
         $stderr.puts "rdoc #{args.join ' '}" if Rake.application.options.trace
         RDoc::RDoc.new.document args
+      rescue SystemExit => exit
+        raise "RDoc coverage is incomplete" unless exit.success?
       end
 
       desc server_task_description