diff --git a/lib/runtime/componentNormalizer.js b/lib/runtime/componentNormalizer.js
index 6e2e9e764..6ece8a8e5 100644
--- a/lib/runtime/componentNormalizer.js
+++ b/lib/runtime/componentNormalizer.js
@@ -62,7 +62,12 @@ export default function normalizeComponent (
     options._ssrRegister = hook
   } else if (injectStyles) {
     hook = shadowMode
-      ? function () { injectStyles.call(this, this.$root.$options.shadowRoot) }
+      ? function () {
+        injectStyles.call(
+          this,
+          (options.functional ? this.parent : this).$root.$options.shadowRoot
+        )
+      }
       : injectStyles
   }