diff --git a/CHANGELOG.md b/CHANGELOG.md
index c5070e3..0294766 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # [develop](https://github.com/adhearsion/electric_slide)
 
+# [0.5.0](https://github.com/adhearsion/electric_slide/compare/v0.4.2...v0.5.0) - [2016-02-12](https://rubygems.org/gems/adhearsion/versions/0.5.0)
+  * API Breakage: Fixed priority strategy now ensures that the same agent cannot be in multiple priorities
+
 # [0.4.2](https://github.com/adhearsion/electric_slide/compare/v0.4.1...v0.4.2) - [2016-02-04](https://rubygems.org/gems/adhearsion/versions/0.4.2)
   * Bugfix: FixedPriority now correctly checks out agents in priority order.
 
diff --git a/lib/electric_slide/agent_strategy/fixed_priority.rb b/lib/electric_slide/agent_strategy/fixed_priority.rb
index 865bb53..b4a4d31 100644
--- a/lib/electric_slide/agent_strategy/fixed_priority.rb
+++ b/lib/electric_slide/agent_strategy/fixed_priority.rb
@@ -37,11 +37,15 @@ def checkout_agent
       end
 
       def <<(agent)
-        # TODO: How aggressively do we check for agents duplicated in multiple priorities?
         raise ArgumentError, "Agents must have a specified priority" unless agent.respond_to?(:priority)
+
         priority = agent.priority || 999999
         @priorities[priority] ||= []
-        @priorities[priority] << agent unless @priorities[priority].include? agent
+
+        unless @priorities[priority].include?(agent)
+          delete(agent)
+          @priorities[priority] << agent
+        end
       end
 
       def delete(agent)
diff --git a/lib/electric_slide/version.rb b/lib/electric_slide/version.rb
index dabeca1..d536b97 100644
--- a/lib/electric_slide/version.rb
+++ b/lib/electric_slide/version.rb
@@ -1,4 +1,4 @@
 # encoding: utf-8
 class ElectricSlide
-  VERSION = '0.4.2'
+  VERSION = '0.5.0'
 end
diff --git a/spec/electric_slide/agent_strategy/fixed_priority_spec.rb b/spec/electric_slide/agent_strategy/fixed_priority_spec.rb
index 90f93ff..8464fc8 100644
--- a/spec/electric_slide/agent_strategy/fixed_priority_spec.rb
+++ b/spec/electric_slide/agent_strategy/fixed_priority_spec.rb
@@ -39,4 +39,25 @@
     subject.checkout_agent
     expect(subject.agent_available?).to be true
   end
+
+  context 'when agents at different priorities are available' do
+    let(:agent1) { agent1 = OpenStruct.new(id: 101, priority: 1) }
+    let(:agent2) { agent1 = OpenStruct.new(id: 102, priority: 2) }
+
+    before do
+      subject << agent1
+      subject << agent2
+    end
+
+    describe 'and the higher priority agent is added again, but at the lowest priority' do
+      before do
+        agent1.priority = 3
+        subject << agent1
+      end
+
+      it 'moves the agent to the new, lower priority' do
+        expect(subject.checkout_agent).to eq(agent2)
+      end
+    end
+  end
 end