diff --git a/CHANGELOG.md b/CHANGELOG.md
index b29632758e..a7c78a82f6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 
 ## Unreleased
 
+* Fix error in LUX script ([PR #3592](https://github.com/alphagov/govuk_publishing_components/pull/3592))
 * Prepend page path when tracking anchor links in GA4 ([PR #3590](https://github.com/alphagov/govuk_publishing_components/pull/3590))
 
 ## 35.15.1
diff --git a/app/assets/javascripts/govuk_publishing_components/vendor/lux/lux-reporter.js b/app/assets/javascripts/govuk_publishing_components/vendor/lux/lux-reporter.js
index 7914928dd8..ef95c59f85 100644
--- a/app/assets/javascripts/govuk_publishing_components/vendor/lux/lux-reporter.js
+++ b/app/assets/javascripts/govuk_publishing_components/vendor/lux/lux-reporter.js
@@ -538,6 +538,10 @@
     // -------------------------------------------------------------------------
     // Settings
     // -------------------------------------------------------------------------
+    // This ID usually appended to the end of the lux.js as a query string when
+    // using the SpeedCurve hosted version - but we have to include it here as
+    // this is self hosted.
+    LUX.customerid = 47044334;
     // Set the sample rate to 1% to avoid all events being sent.
     LUX.samplerate = 1;
     // -------------------------------------------------------------------------
@@ -1494,10 +1498,9 @@
       }
       return getHighPercentileINP();
     }
+    // function simplified for our use, original would get the customerid from the script src URL
+    // but we set it inside the code in this file, so this function just returns that
     function getCustomerId() {
-      if (!LUX.customerid) {
-        LUX.customerid = thisScript.src.match(/id=(\d+)/).pop();
-      }
       return LUX.customerid || "";
     }
     function avgDomDepth() {
@@ -2200,11 +2203,6 @@
   // More settings
   // ---------------------------------------------------------------------------
   //
-  // This ID usually appended to the end of the lux.js as a query string when
-  // using the SpeedCurve hosted version - but we have to include it here as
-  // this is self hosted.
-  LUX.customerid = 47044334;
-
   // Setting debug to `true` shows what happening as it happens. Running
   // `LUX.getDebug()` in the browser's console will show the history of what's
   // happened.
diff --git a/docs/real-user-metrics.md b/docs/real-user-metrics.md
index a9f0ef1c9a..ee3bee47f2 100644
--- a/docs/real-user-metrics.md
+++ b/docs/real-user-metrics.md
@@ -28,9 +28,9 @@ The customer ID is an identifier for the site using LUX, not for the user visiti
 
 When loading `lux.js` from SpeedCurve's CDN, the customer ID is appended to the end of the URI as a query string. The script looks for a script in the DOM with a source of `lux.js`, and from that extracts the customer ID.
 
-Rails adds a fingerprint to the URI which means that `lux.js` becomes (for example) `lux.self-7137780d5344a93190a2c698cd660619d4197420b9b1ef963b639a825a6aa5ff.js` and the script can't find itself.
+Rails adds a fingerprint to the URI which means that `lux.js` becomes (for example) `lux.self-7137780d5344a93190a2c698cd660619d4197420b9b1ef963b639a825a6aa5ff.js` and the script can't find itself. Because of this that part of the script would fail. Instead, we modify the `getCustomerId()` function to simply return `LUX.customerid`.
 
-Because of this the customer ID needs to be set at the end of the `lux.js` file:
+Because of this the customer ID needs to be set in the `lux.js` file:
 
 ```javascript
 LUX.customerid = 47044334