diff --git a/internal/core/runtime/runtime.go b/internal/core/runtime/runtime.go
index 0f303be725..f456980773 100644
--- a/internal/core/runtime/runtime.go
+++ b/internal/core/runtime/runtime.go
@@ -46,6 +46,12 @@ func (r *Runtime) Init() {
 	if r.index != nil {
 		return
 	}
-	r.index = sharedIndex
+	r.index = newIndex()
+
+	// TODO: the builtin-specific instances will ultimately also not be
+	// shared by indexes.
+	r.index.builtinPaths = sharedIndex.builtinPaths
+	r.index.builtinShort = sharedIndex.builtinShort
+
 	r.loaded = map[*build.Instance]interface{}{}
 }