diff --git a/contrib/thermald/README.md b/contrib/thermald/README.md
index e6ed43449..014f3b2f3 100644
--- a/contrib/thermald/README.md
+++ b/contrib/thermald/README.md
@@ -14,4 +14,13 @@ Both XML files (`thermal-conf.xml` and `thermal-cpu-cdev-order-xml`) need to be
 
 Newer thermald versions attempt to automatically load the configuration from ACPI.
 If you want to use a manual configuration with such a version, you may need to remove the `--adaptive` option from the systemd service `ExecStart` line.
-You can do so by overwriting `thermald.service`. This file is present in `/lib/systemd/system/` (it may also be in `/usr/lib/systemd/system/`).
+You can do so by running `sudo systemctl edit thermald.service`.
+
+Note that with `systemctl edit`, before the modified `ExecStart` line, you should add a new line containing `ExecStart=` and nothing on the right, like this:
+
+```
+ExecStart=
+ExecStart=<modified line>
+```
+
+This instructs to replace the existing `ExecStart` instead of adding a new one. Otherwise, you may get an error "Unit thermald.service has a bad unit file setting", and the command `systemctl status thermald.service` may prompt a message "Service has more than one ExecStart= setting".