diff --git a/djblets/extensions/base.py b/djblets/extensions/base.py
--- a/djblets/extensions/base.py
+++ b/djblets/extensions/base.py
@@ -327,6 +327,7 @@ class ExtensionManager(object):
             self.__install_admin_urls(extension)
 
         extension.info.enabled = True
+        settings.INSTALLED_APPS.append(extension.info.app_name)
 
         return extension
 
@@ -338,6 +339,7 @@ class ExtensionManager(object):
                 self._admin_ext_resolver.url_patterns.remove(urlpattern)
 
         extension.info.enabled = False
+        settings.INSTALLED_APPS.remove(extension.info.app_name)
 
         del self._extension_instances[extension.id]