diff --git a/internal/caching/impl_ristretto.go b/internal/caching/impl_ristretto.go
index 677218b5e..01c97ad55 100644
--- a/internal/caching/impl_ristretto.go
+++ b/internal/caching/impl_ristretto.go
@@ -44,9 +44,9 @@ const (
 
 func NewRistrettoCache(maxCost config.DataUnit, maxAge time.Duration, enablePrometheus bool) *Caches {
 	cache, err := ristretto.NewCache(&ristretto.Config{
-		NumCounters: 1e5, // 10x number of expected cache items, affects bloom filter size, gives us room for 10,000 currently
-		BufferItems: 64,  // recommended by the ristretto godocs as a sane buffer size value
-		MaxCost:     int64(maxCost),
+		NumCounters: int64((maxCost / 1024) * 10), // 10 counters per 1KB data, affects bloom filter size
+		BufferItems: 64,                           // recommended by the ristretto godocs as a sane buffer size value
+		MaxCost:     int64(maxCost),               // max cost is in bytes, as per the Dendrite config
 		Metrics:     true,
 		KeyToHash: func(key interface{}) (uint64, uint64) {
 			return z.KeyToHash(key)