diff --git a/lib/pact_broker/api/resources/deployed_versions_for_version_and_environment.rb b/lib/pact_broker/api/resources/deployed_versions_for_version_and_environment.rb
index c1948aea5..9ea4aa20a 100644
--- a/lib/pact_broker/api/resources/deployed_versions_for_version_and_environment.rb
+++ b/lib/pact_broker/api/resources/deployed_versions_for_version_and_environment.rb
@@ -25,6 +25,14 @@ def post_is_create?
           true
         end
 
+        def malformed_request?
+          if request.post?
+            malformed_post_request?
+          else
+            false
+          end
+        end
+
         def create_path
           deployed_version_url(OpenStruct.new(uuid: deployed_version_uuid), base_url)
         end
@@ -67,12 +75,21 @@ def deployed_version_uuid
         end
 
         def replaced_previous_deployed_version
-          params[:replacedPreviousDeployedVersion] == true
+          params(default: {})[:replacedPreviousDeployedVersion]
         end
 
         def title
           "Deployed versions for #{pacticipant_name} version #{pacticipant_version_number}"
         end
+
+        def malformed_post_request?
+          if ![true, false].include?(replaced_previous_deployed_version)
+            set_json_validation_error_messages({ replacedPreviousDeployedVersion: ["must be one of true, false"] })
+            true
+          else
+            false
+          end
+        end
       end
     end
   end
diff --git a/spec/features/record_deployment_spec.rb b/spec/features/record_deployment_spec.rb
index 48dc00f95..329861454 100644
--- a/spec/features/record_deployment_spec.rb
+++ b/spec/features/record_deployment_spec.rb
@@ -19,8 +19,9 @@
       .find{ |relation| relation["name"] == "test" }
       .fetch("href")
   end
+  let(:request_body) { { replacedPreviousDeployedVersion: replaced_previous }.to_json }
 
-  subject { post(path, { replacedPreviousDeployedVersion: replaced_previous }.to_json, headers) }
+  subject { post(path, request_body, headers) }
 
   it { is_expected.to be_a_hal_json_created_response }
 
@@ -33,14 +34,32 @@
   end
 
   it "marks the previous deployment as not currently deployed" do
+    expect { subject }.to change { PactBroker::Deployments::DeployedVersion.currently_deployed.collect(&:uuid) }
+  end
+
+  it "does not change the overall count of currently deployed versions" do
     expect { subject }.to_not change { PactBroker::Deployments::DeployedVersion.currently_deployed.count }
   end
 
+  context "with an empty body" do
+    let(:request_body) { nil }
+
+    it { is_expected.to be_a_json_error_response("must be one of true, false") }
+
+    it "does not change the overall count of currently deployed versions" do
+      expect { subject }.to_not change { PactBroker::Deployments::DeployedVersion.currently_deployed.count }
+    end
+  end
+
   context "when the deployment does not replace the previous deployed version" do
     let(:replaced_previous) { false }
 
     it "leaves the previous deployed version as currently deployed" do
       expect { subject }.to change { PactBroker::Deployments::DeployedVersion.currently_deployed.count }.by(1)
     end
+
+    it "increases the overall count of currently deployed versions" do
+      expect { subject }.to change { PactBroker::Deployments::DeployedVersion.currently_deployed.count }.by(1)
+    end
   end
 end