diff --git a/qutebrowser/browser/browsertab.py b/qutebrowser/browser/browsertab.py
index 7e78b2621..0b1c8d8da 100644
--- a/qutebrowser/browser/browsertab.py
+++ b/qutebrowser/browser/browsertab.py
@@ -812,6 +812,9 @@ class AbstractTab(QWidget):
             self.title_changed.emit(url.toDisplayString())
         self.url_changed.emit(url)
 
+        url = self.url(requested=True)
+        self._update_stylesheet(url)
+
     @pyqtSlot()
     def _on_load_started(self):
         self._progress = 0
diff --git a/qutebrowser/browser/webengine/webenginetab.py b/qutebrowser/browser/webengine/webenginetab.py
index 5f0952bca..101ad3611 100644
--- a/qutebrowser/browser/webengine/webenginetab.py
+++ b/qutebrowser/browser/webengine/webenginetab.py
@@ -801,7 +801,7 @@ class _WebEngineScripts(QObject):
     def _update_stylesheet(self, url=None):
         """Update the custom stylesheet in existing tabs."""
         css = shared.get_user_stylesheet(url=url)
-        code = javascript.assemble('stylesheet', 'set_css', css)
+        code = javascript.assemble('stylesheet', 'set_css', css, delay=True)
         self._tab.run_js_async(code)
 
     def _inject_early_js(self, name, js_code, *,
@@ -1226,9 +1226,6 @@ class WebEngineTab(browsertab.AbstractTab):
             # the old icon is still displayed.
             self.icon_changed.emit(QIcon())
 
-        url = self.url(requested=True)
-        self._update_stylesheet(url)
-
     @pyqtSlot(QUrl)
     def _on_predicted_navigation(self, url):
         """If we know we're going to visit an URL soon, change the settings.
diff --git a/qutebrowser/utils/javascript.py b/qutebrowser/utils/javascript.py
index 93df8e70f..e7053736c 100644
--- a/qutebrowser/utils/javascript.py
+++ b/qutebrowser/utils/javascript.py
@@ -64,14 +64,28 @@ def _convert_js_arg(arg):
             arg, type(arg).__name__))
 
 
-def assemble(module, function, *args):
+def assemble(module, function, *args, delay=False):
     """Assemble a javascript file and a function call."""
     js_args = ', '.join(_convert_js_arg(arg) for arg in args)
     if module == 'window':
         parts = ['window', function]
     else:
         parts = ['window', '_qutebrowser', module, function]
-    code = '"use strict";\n{}({});'.format('.'.join(parts), js_args)
+    if delay:
+        code = '''
+        "use strict";
+        if (document.readyState !== "loading") {{
+            {parts}({args});
+        }} else {{
+            window.addEventListener("DOMContentLoaded", () => {{
+                {parts}({args});
+            }});
+        }}
+        '''
+        code = code.format(parts='.'.join(parts), args=js_args)
+    else:
+        code = '"use strict";\n{}({});'.format('.'.join(parts), js_args)
+    # print(code)
     return code