diff --git a/ext/bg/js/api.js b/ext/bg/js/api.js
index ff5c8abf..82166007 100644
--- a/ext/bg/js/api.js
+++ b/ext/bg/js/api.js
@@ -86,32 +86,7 @@ function apiFrameInformationGet(sender) {
 }
 
 function apiInjectStylesheet(css, sender) {
-    if (!sender.tab) {
-        return Promise.reject(new Error('Invalid tab'));
-    }
-
-    const tabId = sender.tab.id;
-    const frameId = sender.frameId;
-    const details = {
-        code: css,
-        runAt: 'document_start',
-        cssOrigin: 'user',
-        allFrames: false
-    };
-    if (typeof frameId === 'number') {
-        details.frameId = frameId;
-    }
-
-    return new Promise((resolve, reject) => {
-        chrome.tabs.insertCSS(tabId, details, () => {
-            const e = chrome.runtime.lastError;
-            if (e) {
-                reject(new Error(e.message));
-            } else {
-                resolve();
-            }
-        });
-    });
+    return utilBackend()._onApiInjectStylesheet({css}, sender);
 }
 
 async function apiGetEnvironmentInfo() {
diff --git a/ext/bg/js/backend.js b/ext/bg/js/backend.js
index 4b94d073..df021ea2 100644
--- a/ext/bg/js/backend.js
+++ b/ext/bg/js/backend.js
@@ -436,7 +436,32 @@ class Backend {
     }
 
     _onApiInjectStylesheet({css}, sender) {
-        return apiInjectStylesheet(css, sender);
+        if (!sender.tab) {
+            return Promise.reject(new Error('Invalid tab'));
+        }
+
+        const tabId = sender.tab.id;
+        const frameId = sender.frameId;
+        const details = {
+            code: css,
+            runAt: 'document_start',
+            cssOrigin: 'user',
+            allFrames: false
+        };
+        if (typeof frameId === 'number') {
+            details.frameId = frameId;
+        }
+
+        return new Promise((resolve, reject) => {
+            chrome.tabs.insertCSS(tabId, details, () => {
+                const e = chrome.runtime.lastError;
+                if (e) {
+                    reject(new Error(e.message));
+                } else {
+                    resolve();
+                }
+            });
+        });
     }
 
     _onApiGetEnvironmentInfo() {