diff --git a/providers/primitive.rb b/providers/primitive.rb
index 081bf9a..773250a 100644
--- a/providers/primitive.rb
+++ b/providers/primitive.rb
@@ -31,7 +31,8 @@ action :create do
     create_resource(name)
   else
     if @current_resource.agent != new_resource.agent
-      raise "Existing primitive '#{name}' has agent but recipe wanted #{new_resource.agent}"
+      raise "Existing primitive '#{name}' has agent '#{@current_resource.agent}' " \
+            "but recipe wanted '#{new_resource.agent}'"
     end
 
     modify_resource(name)
diff --git a/spec/providers/primitive_spec.rb b/spec/providers/primitive_spec.rb
index 5cdffb0..94cff9d 100644
--- a/spec/providers/primitive_spec.rb
+++ b/spec/providers/primitive_spec.rb
@@ -71,7 +71,19 @@ describe "Chef::Provider::PacemakerPrimitive" do
     end
 
     it "should barf if the primitive has the wrong agent" do
-      pending "not implemented yet"
+      existing_agent = "ocf:openstack:something-else"
+      config = ra[:config].sub(ra[:agent], existing_agent)
+      provider = Chef::Provider::PacemakerPrimitive.new(@resource, @run_context)
+
+      # get_cib_object_definition is invoked by load_current_resource
+      # and later used to see whether to create or modify.
+      expect(provider).to receive(:get_cib_object_definition).and_return(config)
+
+      expected_error = \
+        "Existing primitive '#{ra[:name]}' has agent '#{existing_agent}' " \
+        "but recipe wanted '#{@resource.agent}'"
+      expect { provider.run_action :create }.to \
+        raise_error(RuntimeError, expected_error)
     end
   end
 end