diff --git a/lib/sidekiq/priority.rb b/lib/sidekiq/priority.rb
index 0eaeec4..c901adb 100644
--- a/lib/sidekiq/priority.rb
+++ b/lib/sidekiq/priority.rb
@@ -18,7 +18,7 @@ def self.priorities=(priorities)
     end
 
     def self.queue_with_priority(queue, priority)
-      priority.nil? ? queue : "#{queue}_#{priority}"
+      priority && self.priorities.include?(priority) ? "#{queue}_#{priority}" : queue
     end
   end
 end
diff --git a/spec/sidekiq/worker_ext_spec.rb b/spec/sidekiq/worker_ext_spec.rb
index cfe9895..f98e27c 100644
--- a/spec/sidekiq/worker_ext_spec.rb
+++ b/spec/sidekiq/worker_ext_spec.rb
@@ -22,5 +22,26 @@ def perform(first, second)
         'queue' => 'foo_high'
       }
     end
+
+    it 'sends an item to the default queue if priority is nil' do
+      TestWorker.stub(:client_push) { |item| item }
+      item = TestWorker.perform_with_priority(:invalid_priority, 1, 2)
+      item.should == {
+          'class' => TestWorker,
+          'args' => [1, 2],
+          'queue' => :foo
+      }
+    end
+
+    it 'sends an item to the default queue if a random priority is given' do
+      TestWorker.stub(:client_push) { |item| item }
+      item = TestWorker.perform_with_priority(:random_priority, 1, 2)
+      item.should == {
+          'class' => TestWorker,
+          'args' => [1, 2],
+          'queue' => :foo
+      }
+    end
+
   end
 end