diff --git a/src/lib/components/tabs/Tab.svelte b/src/lib/components/tabs/Tab.svelte
index 8f59897..94002ef 100644
--- a/src/lib/components/tabs/Tab.svelte
+++ b/src/lib/components/tabs/Tab.svelte
@@ -97,6 +97,9 @@
     tabIndex: selected ? 0 : -1,
     disabled: disabled ? true : undefined,
   };
+  $: if (process.env.NODE_ENV === "test") {
+    Object.assign(propsWeControl, { ["data-headlessui-index"]: myIndex });
+  }
 
   $: slotProps = { selected };
 </script>
diff --git a/src/lib/components/tabs/TabPanel.svelte b/src/lib/components/tabs/TabPanel.svelte
index 972c351..d8284b8 100644
--- a/src/lib/components/tabs/TabPanel.svelte
+++ b/src/lib/components/tabs/TabPanel.svelte
@@ -33,6 +33,10 @@
     "aria-labelledby": $api.tabs[myIndex]?.id,
     tabIndex: selected ? 0 : -1,
   };
+
+  $: if (process.env.NODE_ENV === "test") {
+    Object.assign(propsWeControl, { ["data-headlessui-index"]: myIndex });
+  }
 </script>
 
 <Render