diff --git a/app/controllers/lti_api_controller.rb b/app/controllers/lti_api_controller.rb
index 88b0d4ed7aa..9262e80eaf0 100644
--- a/app/controllers/lti_api_controller.rb
+++ b/app/controllers/lti_api_controller.rb
@@ -77,8 +77,8 @@ class LtiApiController < ApplicationController
   #   }
   # }
   #
-  # * result.duration must be an ISO 8601 duration
   # * object.id will be logged as url
+  # * result.duration must be an ISO 8601 duration if supplied
   def xapi_service
     token = Lti::XapiService::Token.parse_and_validate(params[:token])
     verify_oauth(token.tool)
diff --git a/app/models/lti/xapi_service.rb b/app/models/lti/xapi_service.rb
index 8cd15247055..907954abeab 100644
--- a/app/models/lti/xapi_service.rb
+++ b/app/models/lti/xapi_service.rb
@@ -36,10 +36,13 @@ module Lti
       course = token.course
       user = token.user
       tool = token.tool
-      duration = params[:result]['duration']
-      seconds = Duration.new(duration).to_i
+      duration = params[:result] ? params[:result]['duration'] : nil
+      seconds = duration ? Duration.new(duration).to_i : nil
 
-      course.enrollments.where(:user_id => user).update_all(['total_activity_time = COALESCE(total_activity_time, 0) + ?', seconds])
+      if duration
+        course.enrollments.where(:user_id => user).
+          update_all(['total_activity_time = COALESCE(total_activity_time, 0) + ?', seconds])
+      end
 
       access = AssetUserAccess.where(user_id: user, asset_code: tool.asset_string).first_or_initialize
       access.log(course, group_code: "external_tools", category: "external_tools")
diff --git a/spec/apis/lti/xapi_service_spec.rb b/spec/apis/lti/xapi_service_spec.rb
index 0d0a233b698..8349f483e04 100644
--- a/spec/apis/lti/xapi_service_spec.rb
+++ b/spec/apis/lti/xapi_service_spec.rb
@@ -101,4 +101,11 @@ describe LtiApiController, type: :request do
 
     after { Setting.set 'enable_page_views', 'false' }
   end
+
+  it "should handle requests without durations" do
+    body = xapi_body
+    body.delete(:result)
+    make_call('body' => body)
+    expect(response).to be_success
+  end
 end