diff --git a/src/govuk/components/header/header.mjs b/src/govuk/components/header/header.mjs
index 5f9bcbc356..0e03a309b4 100644
--- a/src/govuk/components/header/header.mjs
+++ b/src/govuk/components/header/header.mjs
@@ -102,7 +102,7 @@ export class Header extends GOVUKFrontendComponent {
     if (!breakpoint.value) {
       throw new ElementError({
         componentName: 'Header',
-        identifier: `CSS custom property (\`${breakpoint.property}\`)`
+        identifier: `CSS custom property (\`${breakpoint.property}\`) on pseudo-class \`:root\``
       })
     }
 
diff --git a/src/govuk/components/tabs/tabs.mjs b/src/govuk/components/tabs/tabs.mjs
index 6358d114de..907c8a2e42 100644
--- a/src/govuk/components/tabs/tabs.mjs
+++ b/src/govuk/components/tabs/tabs.mjs
@@ -110,7 +110,7 @@ export class Tabs extends GOVUKFrontendComponent {
     if (!breakpoint.value) {
       throw new ElementError({
         componentName: 'Tabs',
-        identifier: `CSS custom property (\`${breakpoint.property}\`)`
+        identifier: `CSS custom property (\`${breakpoint.property}\`) on pseudo-class \`:root\``
       })
     }