diff --git a/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/state/PendingBlocks.java b/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/state/PendingBlocks.java
index d00c1ce482..dc0cce5dd2 100644
--- a/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/state/PendingBlocks.java
+++ b/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/state/PendingBlocks.java
@@ -12,6 +12,8 @@
  */
 package tech.pegasys.pantheon.ethereum.eth.sync.state;
 
+import static java.util.Collections.newSetFromMap;
+
 import tech.pegasys.pantheon.ethereum.core.Block;
 import tech.pegasys.pantheon.ethereum.core.Hash;
 
@@ -23,8 +25,6 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
-import io.netty.util.internal.ConcurrentSet;
-
 public class PendingBlocks {
 
   private final Map<Hash, Block> pendingBlocks = new ConcurrentHashMap<>();
@@ -47,7 +47,7 @@ public boolean registerPendingBlock(final Block pendingBlock) {
         .computeIfAbsent(
             pendingBlock.getHeader().getParentHash(),
             h -> {
-              final ConcurrentSet<Hash> set = new ConcurrentSet<>();
+              final Set<Hash> set = newSetFromMap(new ConcurrentHashMap<>());
               // Go ahead and add our value at construction, so that we don't set an empty set which
               // could be removed in deregisterPendingBlock
               set.add(pendingBlock.getHash());