diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 77a3fe6cd..cec6b3e54 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -387,9 +387,9 @@ retention:
   #
   # The rationale for this per-job configuration is that some rooms might have a
   # retention policy with a low 'max_lifetime', where history needs to be purged
-  # of outdated messages on a more frequent basis (e.g. every 12h), but not want
-  # that purge to be performed by a job that's iterating over every room it knows,
-  # which could be heavy on the server.
+  # of outdated messages on a more frequent basis than for the rest of the rooms
+  # (e.g. every 12h), but not want that purge to be performed by a job that's
+  # iterating over every room it knows, which could be heavy on the server.
   #
   #purge_jobs:
   #  - shortest_max_lifetime: 1d
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 11ff55922..9ac112233 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -948,9 +948,9 @@ class ServerConfig(Config):
           #
           # The rationale for this per-job configuration is that some rooms might have a
           # retention policy with a low 'max_lifetime', where history needs to be purged
-          # of outdated messages on a more frequent basis (e.g. every 12h), but not want
-          # that purge to be performed by a job that's iterating over every room it knows,
-          # which could be heavy on the server.
+          # of outdated messages on a more frequent basis than for the rest of the rooms
+          # (e.g. every 12h), but not want that purge to be performed by a job that's
+          # iterating over every room it knows, which could be heavy on the server.
           #
           #purge_jobs:
           #  - shortest_max_lifetime: 1d