diff --git a/changelog.d/14221.misc b/changelog.d/14221.misc
new file mode 100644
index 0000000000..fe7afac245
--- /dev/null
+++ b/changelog.d/14221.misc
@@ -0,0 +1 @@
+Rename the `cache_memory` extra to `cache-memory`, for compatability with poetry-core 1.3.0 and [PEP 685](https://peps.python.org/pep-0685/). From-source installations using this extra will need to install using the new name.
diff --git a/pyproject.toml b/pyproject.toml
index 7fbbc08915..8bc24c556a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -227,7 +227,7 @@ jwt = ["authlib"]
 # (if it is not installed, we fall back to slow code.)
 redis = ["txredisapi", "hiredis"]
 # Required to use experimental `caches.track_memory_usage` config option.
-cache_memory = ["pympler"]
+cache-memory = ["pympler"]
 test = ["parameterized", "idna"]
 
 # The duplication here is awful. I hate hate hate hate hate it. However, for now I want
@@ -258,7 +258,7 @@ all = [
     "jaeger-client", "opentracing",
     # redis
     "txredisapi", "hiredis",
-    # cache_memory
+    # cache-memory
     "pympler",
     # omitted:
     #   - test: it's useful to have this separate from dev deps in the olddeps job
diff --git a/synapse/config/cache.py b/synapse/config/cache.py
index 2db8cfb005..eb4194a5a9 100644
--- a/synapse/config/cache.py
+++ b/synapse/config/cache.py
@@ -159,7 +159,7 @@ class CacheConfig(Config):
 
         self.track_memory_usage = cache_config.get("track_memory_usage", False)
         if self.track_memory_usage:
-            check_requirements("cache_memory")
+            check_requirements("cache-memory")
 
         expire_caches = cache_config.get("expire_caches", True)
         cache_entry_ttl = cache_config.get("cache_entry_ttl", "30m")