diff --git a/platform/chromium/vapi-background.js b/platform/chromium/vapi-background.js
index 36fdf742b..077211831 100644
--- a/platform/chromium/vapi-background.js
+++ b/platform/chromium/vapi-background.js
@@ -1024,22 +1024,29 @@ vAPI.messaging = {
         }
         case 'userCSS':
             if ( tabId === undefined ) { break; }
-            const details = {
-                code: undefined,
-                frameId: portDetails.frameId,
-                matchAboutBlank: true
-            };
-            if ( msg.add ) {
-                details.runAt = 'document_start';
-            }
             const promises = [];
-            for ( const cssText of msg.add ) {
-                details.code = cssText;
-                promises.push(vAPI.tabs.insertCSS(tabId, details));
+            if ( msg.add ) {
+                const details = {
+                    code: undefined,
+                    frameId: portDetails.frameId,
+                    matchAboutBlank: true,
+                    runAt: 'document_start',
+                };
+                for ( const cssText of msg.add ) {
+                    details.code = cssText;
+                    promises.push(vAPI.tabs.insertCSS(tabId, details));
+                }
             }
-            for ( const cssText of msg.remove ) {
-                details.code = cssText;
-                promises.push(vAPI.tabs.removeCSS(tabId, details));
+            if ( msg.remove ) {
+                const details = {
+                    code: undefined,
+                    frameId: portDetails.frameId,
+                    matchAboutBlank: true,
+                };
+                for ( const cssText of msg.remove ) {
+                    details.code = cssText;
+                    promises.push(vAPI.tabs.removeCSS(tabId, details));
+                }
             }
             Promise.all(promises).then(( ) => {
                 callback();