diff --git a/daphne/server.py b/daphne/server.py
index 7cdd61e..8390527 100755
--- a/daphne/server.py
+++ b/daphne/server.py
@@ -1,6 +1,15 @@
 # This has to be done first as Twisted is import-order-sensitive with reactors
+import sys  # isort:skip
+import warnings  # isort:skip
 from twisted.internet import asyncioreactor  # isort:skip
-asyncioreactor.install()  # isort:skip
+if "twisted.internet.reactor" in sys.modules:
+    warnings.warn(
+        "Something has already installed a Twisted reactor. Attempting to uninstall it; ",
+        "you can fix this warning by importing daphne.server early in your codebase or ",
+        "finding the package that imports Twisted and importing it later on."
+    )
+    del sys.modules["twisted.internet.reactor"]
+asyncioreactor.install()
 
 import asyncio
 import logging