diff --git a/changelog.d/9270.misc b/changelog.d/9270.misc
new file mode 100644
index 000000000..908e5ee78
--- /dev/null
+++ b/changelog.d/9270.misc
@@ -0,0 +1 @@
+Restore PyPy compatibility by not calling CPython-specific GC methods when under PyPy.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 395e202b8..9840a9d55 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -16,6 +16,7 @@
 import gc
 import logging
 import os
+import platform
 import signal
 import socket
 import sys
@@ -339,7 +340,7 @@ async def start(hs: "synapse.server.HomeServer", listeners: Iterable[ListenerCon
     # rest of time. Doing so means less work each GC (hopefully).
     #
     # This only works on Python 3.7
-    if sys.version_info >= (3, 7):
+    if platform.python_implementation() == "CPython" and sys.version_info >= (3, 7):
         gc.collect()
         gc.freeze()