diff --git a/.changeset/fix-tabs-active-indicator-disappearing.md b/.changeset/fix-tabs-active-indicator-disappearing.md
new file mode 100644
index 0000000000..c8537940c9
--- /dev/null
+++ b/.changeset/fix-tabs-active-indicator-disappearing.md
@@ -0,0 +1,7 @@
+---
+'@backstage/ui': patch
+---
+
+Fixed an issue where the active tab indicator would disappear shortly after page load for uncontrolled Tabs.
+
+**Affected components:** Tabs
diff --git a/packages/ui/src/components/Tabs/TabsIndicators.tsx b/packages/ui/src/components/Tabs/TabsIndicators.tsx
index aef792310e..400ecf82c2 100644
--- a/packages/ui/src/components/Tabs/TabsIndicators.tsx
+++ b/packages/ui/src/components/Tabs/TabsIndicators.tsx
@@ -32,6 +32,12 @@ export const TabsIndicators = (props: TabsIndicatorsProps) => {
   const prevSelectedKey = useRef<string | null>(null);
 
   const updateCSSVariables = useCallback(() => {
+    // When rendered inside CollectionBuilder's hidden tree (for collection
+    // building), there is no TabListStateContext provider, so state is null.
+    // Bail out to avoid overwriting CSS variables on the shared tabsRef DOM
+    // element that the real instance also writes to.
+    if (state == null) return;
+
     if (!tabsRef.current) return;
 
     const tabsRect = tabsRef.current.getBoundingClientRect();