Testing this fix is a little tricky as there is no graph in core Moodle that uses a line type = brush . We initially found this issue when using adaptivequiz plugin. Here is the testing instruction but we are open to providing another way if required (e.g.: Script to simulate the graph or an example of a plugin that displays a graph with the issue). Log in as admin. main and 404 - You need to enable the Survey activity in Site admin > Plugins > Manage activities Create a course. Create a survey in the course. The " COLLES (Actual) " survey type should be okay for this issue. On a different browser session, log in as a student enrolled in the course and complete the survey. Download and apply the first test patch 0001-MDL-79215-TEST-1.patch to your Moodle instance. git am -3 path /to/0001-MDL-79215-TEST-1 .patch Back on the admin's browser window, navigate to the survey's Response reports page. Confirm that the graph is rendered and you don't encounter any errors. Reset your instance so that the first test patch gets dropped. Download and apply the second test patch 0002-MDL-79215-TEST-2.patch git am -3 path /to/0002-MDL-79215-TEST-2 .patch Confirm that the graph is rendered and you don't encounter any errors.