diff --git a/changelog.d/12652.misc b/changelog.d/12652.misc
new file mode 100644
index 000000000000..7b7c1cf5ff2a
--- /dev/null
+++ b/changelog.d/12652.misc
@@ -0,0 +1 @@
+Move `pympler` back in to the `all` extras.
diff --git a/debian/build_virtualenv b/debian/build_virtualenv
index d2955f762845..f1ec60916325 100755
--- a/debian/build_virtualenv
+++ b/debian/build_virtualenv
@@ -41,7 +41,6 @@ poetry export \
     --extras all \
     --extras test \
     --extras systemd \
-    --extras cache_memory \
     -o exported_requirements.txt
 deactivate
 rm -rf "$TEMP_VENV"
diff --git a/poetry.lock b/poetry.lock
index 89e78576b7b6..0fc6cef35582 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1545,7 +1545,7 @@ docs = ["sphinx", "repoze.sphinx.autointerface"]
 test = ["zope.i18nmessageid", "zope.testing", "zope.testrunner"]
 
 [extras]
-all = ["matrix-synapse-ldap3", "psycopg2", "psycopg2cffi", "psycopg2cffi-compat", "pysaml2", "authlib", "lxml", "sentry-sdk", "jaeger-client", "opentracing", "pyjwt", "txredisapi", "hiredis"]
+all = ["matrix-synapse-ldap3", "psycopg2", "psycopg2cffi", "psycopg2cffi-compat", "pysaml2", "authlib", "lxml", "sentry-sdk", "jaeger-client", "opentracing", "pyjwt", "txredisapi", "hiredis", "Pympler"]
 cache_memory = ["Pympler"]
 jwt = ["pyjwt"]
 matrix-synapse-ldap3 = ["matrix-synapse-ldap3"]
@@ -1562,7 +1562,7 @@ url_preview = ["lxml"]
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.7.1"
-content-hash = "2bda1a7cfc8cc02832b4a7d16bf7e1615cb05e0639bdb30688aadf692d851942"
+content-hash = "93e7f4eff6dd0a853847e27d7b28ac1e389346b0df181da7a68e7dfd2fc4d473"
 
 [metadata.files]
 attrs = [
diff --git a/pyproject.toml b/pyproject.toml
index 446895711b01..05e43e1b3662 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -231,10 +231,11 @@ all = [
     "jaeger-client", "opentracing",
     # jwt
     "pyjwt",
-    #redis
-    "txredisapi", "hiredis"
+    # redis
+    "txredisapi", "hiredis",
+    # cache_memory
+    "pympler",
     # omitted:
-    #   - cache_memory: this is an experimental option
     #   - test: it's useful to have this separate from dev deps in the olddeps job
     #   - systemd: this is a system-based requirement
 ]