diff --git a/libp2p/protocols/pubsub/pubsubpeer.nim b/libp2p/protocols/pubsub/pubsubpeer.nim
index 745dd01..2d9ef3f 100644
--- a/libp2p/protocols/pubsub/pubsubpeer.nim
+++ b/libp2p/protocols/pubsub/pubsubpeer.nim
@@ -9,7 +9,8 @@
 
 import options, sets, hashes, strutils
 import chronos, chronicles
-import rpcmsg,
+import rpcmsg, 
+       timedcache,
        ../../peer,
        ../../peerinfo,
        ../../connection,
@@ -21,12 +22,12 @@ logScope:
 
 type
     PubSubPeer* = ref object of RootObj
+      id*: string # base58 peer id string
       peerInfo*: PeerInfo
       conn*: Connection
       handler*: RPCHandler
       topics*: seq[string]
-      id*: string # base58 peer id string
-      seen: HashSet[string] # list of messages forwarded to peers
+      seen: TimedCache[string] # list of messages forwarded to peers
 
     RPCHandler* = proc(peer: PubSubPeer, msg: seq[RPCMsg]): Future[void] {.gcsafe.}
 
@@ -64,7 +65,7 @@ proc send*(p: PubSubPeer, msgs: seq[RPCMsg]) {.async, gcsafe.} =
 
     trace "sending encoded msgs to peer", peer = p.id, encoded = encodedHex
     await p.conn.writeLp(encoded.buffer)
-    p.seen.incl(encodedHex)
+    p.seen.put(encodedHex)
 
 proc newPubSubPeer*(conn: Connection, handler: RPCHandler): PubSubPeer =
   new result
@@ -72,4 +73,4 @@ proc newPubSubPeer*(conn: Connection, handler: RPCHandler): PubSubPeer =
   result.conn = conn
   result.peerInfo = conn.peerInfo
   result.id = conn.peerInfo.peerId.get().pretty()
-  result.seen = initSet[string]()
+  result.seen = newTimedCache[string]()
diff --git a/libp2p/protocols/pubsub/rpcmsg.nim b/libp2p/protocols/pubsub/rpcmsg.nim
index 6fb3444..9ca5f3a 100644
--- a/libp2p/protocols/pubsub/rpcmsg.nim
+++ b/libp2p/protocols/pubsub/rpcmsg.nim
@@ -9,7 +9,7 @@
 
 import sequtils, options
 import chronos, nimcrypto/sysrand, chronicles
-import ../../peerinfo, 
+import ../../peerinfo,
        ../../peer,
        ../../crypto/crypto,
        ../../protobuf/minprotobuf
diff --git a/libp2p/protocols/pubsub/timedcache.nim b/libp2p/protocols/pubsub/timedcache.nim
new file mode 100644
index 0000000..8b40e25
--- /dev/null
+++ b/libp2p/protocols/pubsub/timedcache.nim
@@ -0,0 +1,56 @@
+## Nim-LibP2P
+## Copyright (c) 2019 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+import tables, hashes
+import chronos, chronicles
+
+logScope:
+  topic = "TimedCache"
+
+const Timeout* = 5 * 1000 # default timeout in ms
+
+type
+  ExpireHandler*[V] = proc(val: V) {.gcsafe.}
+  TimedEntry*[V] = object of RootObj
+    val: V
+    handler: ExpireHandler[V]
+
+  TimedCache*[V] = ref object of RootObj
+    cache*: Table[string, TimedEntry[V]]
+    onExpire*: ExpireHandler[V]
+
+proc newTimedCache*[V](): TimedCache[V] =
+  new result
+  result.cache = initTable[string, TimedEntry[V]]()
+
+proc put*[V](t: TimedCache[V],
+             key: string,
+             val: V = "",
+             timeout: uint64 = Timeout,
+             handler: ExpireHandler[V] = nil) = 
+  trace "adding entry to timed cache", key = key, val = val
+  t.cache[key] = TimedEntry[V](val: val, handler: handler)
+
+  # TODO: addTimer with param Duration is missing from chronos, needs to be added
+  addTimer(
+    timeout,
+    proc (arg: pointer = nil) {.gcsafe.} =
+      trace "deleting expired entry from timed cache", key = key, val = val
+      var entry = t.cache[key]
+      t.cache.del(key)
+      if not isNil(entry.handler):
+        entry.handler(entry.val)
+  )
+
+proc contains*[V](t: TimedCache[V], key: string): bool = 
+  t.cache.contains(key)
+
+proc del*[V](t: TimedCache[V], key: string) =
+  trace "deleting entry from timed cache", key = key
+  t.cache.del(key)