diff --git a/qa/rpc-tests/p2p-compactblocks.py b/qa/rpc-tests/p2p-compactblocks.py
index ab4b809dedd63..fc1f16c6d2a05 100755
--- a/qa/rpc-tests/p2p-compactblocks.py
+++ b/qa/rpc-tests/p2p-compactblocks.py
@@ -764,6 +764,54 @@ def request_cb_announcements(self, peer, node, version):
         msg.announce = True
         peer.send_and_ping(msg)
 
+    def test_compactblock_reconstruction_multiple_peers(self, node, stalling_peer, delivery_peer):
+        assert(len(self.utxos))
+
+        def announce_cmpct_block(node, peer):
+            utxo = self.utxos.pop(0)
+            block = self.build_block_with_transactions(node, utxo, 5)
+
+            cmpct_block = HeaderAndShortIDs()
+            cmpct_block.initialize_from_block(block)
+            msg = msg_cmpctblock(cmpct_block.to_p2p())
+            peer.send_and_ping(msg)
+            with mininode_lock:
+                assert(peer.last_getblocktxn is not None)
+            return block, cmpct_block
+
+        block, cmpct_block = announce_cmpct_block(node, stalling_peer)
+
+        for tx in block.vtx[1:]:
+            delivery_peer.send_message(msg_tx(tx))
+        delivery_peer.sync_with_ping()
+        mempool = node.getrawmempool()
+        for tx in block.vtx[1:]:
+            assert(tx.hash in mempool)
+
+        delivery_peer.send_and_ping(msg_cmpctblock(cmpct_block.to_p2p()))
+        assert_equal(int(node.getbestblockhash(), 16), block.sha256)
+
+        self.utxos.append([block.vtx[-1].sha256, 0, block.vtx[-1].vout[0].nValue])
+
+        # Now test that delivering an invalid compact block won't break relay
+
+        block, cmpct_block = announce_cmpct_block(node, stalling_peer)
+        for tx in block.vtx[1:]:
+            delivery_peer.send_message(msg_tx(tx))
+        delivery_peer.sync_with_ping()
+
+        cmpct_block.prefilled_txn[0].tx.wit.vtxinwit = [ CTxInWitness() ]
+        cmpct_block.prefilled_txn[0].tx.wit.vtxinwit[0].scriptWitness.stack = [ser_uint256(0)]
+
+        cmpct_block.use_witness = True
+        delivery_peer.send_and_ping(msg_cmpctblock(cmpct_block.to_p2p()))
+        assert(int(node.getbestblockhash(), 16) != block.sha256)
+
+        msg = msg_blocktxn()
+        msg.block_transactions.blockhash = block.sha256
+        msg.block_transactions.transactions = block.vtx[1:]
+        stalling_peer.send_and_ping(msg)
+        assert_equal(int(node.getbestblockhash(), 16), block.sha256)
 
     def run_test(self):
         # Setup the p2p connections and start up the network thread.
@@ -848,6 +896,10 @@ def run_test(self):
         self.test_invalid_tx_in_compactblock(self.nodes[1], self.segwit_node, False)
         self.test_invalid_tx_in_compactblock(self.nodes[1], self.old_node, False)
 
+        print("\tTesting reconstructing compact blocks from all peers...")
+        self.test_compactblock_reconstruction_multiple_peers(self.nodes[1], self.segwit_node, self.old_node)
+        sync_blocks(self.nodes)
+
         # Advance to segwit activation
         print ("\nAdvancing to segwit activation\n")
         self.activate_segwit(self.nodes[1])
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index a4e5ad2095cb8..e10694ed1811f 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1782,6 +1782,11 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             }
         }
 
+        // Keep a CBlock for "optimistic" compactblock reconstructions (see
+        // below)
+        std::shared_ptr<CBlock> pblock = std::make_shared<CBlock>();
+        bool fBlockReconstructed = false;
+
         LOCK(cs_main);
         // If AcceptBlockHeader returned true, it set pindex
         assert(pindex);
@@ -1870,6 +1875,23 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     req.blockhash = pindex->GetBlockHash();
                     connman.PushMessage(pfrom, msgMaker.Make(NetMsgType::GETBLOCKTXN, req));
                 }
+            } else {
+                // This block is either already in flight from a different
+                // peer, or this peer has too many blocks outstanding to
+                // download from.
+                // Optimistically try to reconstruct anyway since we might be
+                // able to without any round trips.
+                PartiallyDownloadedBlock tempBlock(&mempool);
+                ReadStatus status = tempBlock.InitData(cmpctblock);
+                if (status != READ_STATUS_OK) {
+                    // TODO: don't ignore failures
+                    return true;
+                }
+                std::vector<CTransactionRef> dummy;
+                status = tempBlock.FillBlock(*pblock, dummy);
+                if (status == READ_STATUS_OK) {
+                    fBlockReconstructed = true;
+                }
             }
         } else {
             if (fAlreadyInFlight) {
@@ -1889,6 +1911,29 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 return ProcessMessage(pfrom, NetMsgType::HEADERS, vHeadersMsg, nTimeReceived, chainparams, connman);
             }
         }
+
+        if (fBlockReconstructed) {
+            // If we got here, we were able to optimistically reconstruct a
+            // block that is in flight from some other peer.
+            {
+                LOCK(cs_main);
+                mapBlockSource.emplace(pblock->GetHash(), std::make_pair(pfrom->GetId(), false));
+            }
+            bool fNewBlock = false;
+            ProcessNewBlock(chainparams, pblock, true, &fNewBlock);
+            if (fNewBlock)
+                pfrom->nLastBlockTime = GetTime();
+
+            LOCK(cs_main); // hold cs_main for CBlockIndex::IsValid()
+            if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS)) {
+                // Clear download state for this block, which is in
+                // process from some other peer.  We do this after calling
+                // ProcessNewBlock so that a malleated cmpctblock announcement
+                // can't be used to interfere with block relay.
+                MarkBlockAsReceived(pblock->GetHash());
+            }
+        }
+
     }
 
     else if (strCommand == NetMsgType::BLOCKTXN && !fImporting && !fReindex) // Ignore blocks received while importing