diff --git chrome/browser/themes/theme_service.cc chrome/browser/themes/theme_service.cc
index dbd628982e216..d77a39111e254 100644
--- chrome/browser/themes/theme_service.cc
+++ chrome/browser/themes/theme_service.cc
@@ -29,6 +29,7 @@
 #include "base/task/thread_pool.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
+#include "cef/libcef/features/runtime.h"
 #include "chrome/browser/browser_features.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/theme_installed_infobar_delegate.h"
@@ -69,6 +70,10 @@
 #include "ui/color/color_provider_manager.h"
 #include "ui/native_theme/native_theme.h"
 
+#if BUILDFLAG(ENABLE_CEF)
+#include "cef/libcef/common/extensions/extensions_util.h"
+#endif
+
 #if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "base/scoped_observation.h"
 #include "extensions/browser/extension_registry_observer.h"
@@ -270,11 +275,19 @@ void ThemeService::Init() {
   // OnExtensionServiceReady. Otherwise, the ThemeObserver won't be
   // constructed in time to observe the corresponding events.
 #if BUILDFLAG(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_CEF)
+  const bool extensions_disabled = cef::IsAlloyRuntimeEnabled() &&
+                                   !extensions::ExtensionsEnabled();
+#else
+  const bool extensions_disabled = false;
+#endif
+  if (!extensions_disabled) {
   theme_observer_ = std::make_unique<ThemeObserver>(this);
 
   extensions::ExtensionSystem::Get(profile_)->ready().Post(
       FROM_HERE, base::BindOnce(&ThemeService::OnExtensionServiceReady,
                                 weak_ptr_factory_.GetWeakPtr()));
+  }
 #endif
   theme_syncable_service_ =
       std::make_unique<ThemeSyncableService>(profile_, this);
diff --git chrome/browser/themes/theme_service_factory.cc chrome/browser/themes/theme_service_factory.cc
index 879bbeef4037b..e6cc36f388197 100644
--- chrome/browser/themes/theme_service_factory.cc
+++ chrome/browser/themes/theme_service_factory.cc
@@ -9,6 +9,7 @@
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"
+#include "cef/libcef/features/runtime.h"
 #include "chrome/browser/extensions/extension_system_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/themes/theme_service.h"
@@ -35,6 +36,10 @@
 #include "ui/linux/linux_ui_factory.h"
 #endif
 
+#if BUILDFLAG(ENABLE_CEF)
+#include "cef/libcef/common/extensions/extensions_util.h"
+#endif
+
 namespace {
 
 const ThemeHelper& GetThemeHelper() {
@@ -96,7 +101,15 @@ ThemeServiceFactory::ThemeServiceFactory()
               .Build()) {
   DependsOn(extensions::ExtensionRegistryFactory::GetInstance());
   DependsOn(extensions::ExtensionPrefsFactory::GetInstance());
+#if BUILDFLAG(ENABLE_CEF)
+  const bool extensions_disabled = cef::IsAlloyRuntimeEnabled() &&
+                                   !extensions::ExtensionsEnabled();
+#else
+  const bool extensions_disabled = false;
+#endif
+  if (!extensions_disabled) {
   DependsOn(extensions::ExtensionSystemFactory::GetInstance());
+  }
 }
 
 ThemeServiceFactory::~ThemeServiceFactory() = default;