diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 803b9d599d..30a9e3f0a3 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -58,7 +58,7 @@ cache_counter = metrics.register_cache(
 
 class Cache(object):
 
-    def __init__(self, name, max_entries=1000, keylen=1, lru=False):
+    def __init__(self, name, max_entries=1000, keylen=1, lru=True):
         if lru:
             self.cache = LruCache(max_size=max_entries)
             self.max_entries = None
@@ -158,7 +158,7 @@ class CacheDescriptor(object):
     which can be used to insert values into the cache specifically, without
     calling the calculation function.
     """
-    def __init__(self, orig, max_entries=1000, num_args=1, lru=False):
+    def __init__(self, orig, max_entries=1000, num_args=1, lru=True):
         self.orig = orig
 
         self.max_entries = max_entries
@@ -209,7 +209,7 @@ class CacheDescriptor(object):
         return wrapped
 
 
-def cached(max_entries=1000, num_args=1, lru=False):
+def cached(max_entries=1000, num_args=1, lru=True):
     return lambda orig: CacheDescriptor(
         orig,
         max_entries=max_entries,
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 4db07f6fb4..55dd3f6cfb 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -78,7 +78,7 @@ class RoomMemberStore(SQLBaseStore):
             lambda events: events[0] if events else None
         )
 
-    @cached()
+    @cached(max_entries=5000)
     def get_users_in_room(self, room_id):
         def f(txn):
 
@@ -154,7 +154,7 @@ class RoomMemberStore(SQLBaseStore):
             RoomsForUser(**r) for r in self.cursor_to_dict(txn)
         ]
 
-    @cached()
+    @cached(max_entries=5000)
     def get_joined_hosts_for_room(self, room_id):
         return self.runInteraction(
             "get_joined_hosts_for_room",