diff --git a/src/index.ts b/src/index.ts
index f7bd969..a4a3a58 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,19 +1,13 @@
-export function injectStyles(
-  shadowRootElement: HTMLElement,
-  insertBeforeSelector: string,
-  styles: string
-) {
+export function injectStyles(shadowRootElement: HTMLElement, insertBeforeSelector: string, styles: string) {
   const root = shadowRootElement.shadowRoot;
-  let styleAlreadyAdded = false;
-  const currentStyleTags = Array.from(root.querySelectorAll('style'));
-  currentStyleTags.forEach((element: HTMLStyleElement, index) => {
-    if (element.innerHTML === styles) {
-      styleAlreadyAdded = true;
-    }
-    if (currentStyleTags.length - 1 === index && styleAlreadyAdded === false) {
+
+  if (root !== null) {
+    const styleElements = root.querySelectorAll('style');
+
+    if (!Array.from(styleElements).some(el => el.innerHTML === styles)) {
       const newStyleTag = document.createElement('style');
       newStyleTag.innerHTML = styles;
       root.insertBefore(newStyleTag, root.querySelector(insertBeforeSelector));
     }
-  });
+  }
 }