diff --git a/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManager.java b/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManager.java
index 0d482a69a1..2157502cff 100644
--- a/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManager.java
+++ b/ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManager.java
@@ -39,9 +39,11 @@ import tech.pegasys.pantheon.metrics.OperationTimer;
 import tech.pegasys.pantheon.util.uint.UInt256;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
@@ -49,7 +51,6 @@ import java.util.stream.Collectors;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Range;
-import io.netty.util.internal.ConcurrentSet;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
@@ -65,7 +66,8 @@ public class BlockPropagationManager<C> {
 
   private final AtomicBoolean started = new AtomicBoolean(false);
 
-  private final Set<Hash> requestedBlocks = new ConcurrentSet<>();
+  private final Set<Hash> requestedBlocks = Collections.newSetFromMap(new ConcurrentHashMap<>());
+  private final Set<Hash> importingBlocks = Collections.newSetFromMap(new ConcurrentHashMap<>());
   private final PendingBlocks pendingBlocks;
 
   BlockPropagationManager(
@@ -202,6 +204,9 @@ public class BlockPropagationManager<C> {
         if (pendingBlocks.contains(announcedBlock.hash())) {
           continue;
         }
+        if (importingBlocks.contains(announcedBlock.hash())) {
+          continue;
+        }
         if (blockchain.contains(announcedBlock.hash())) {
           continue;
         }
@@ -247,6 +252,17 @@ public class BlockPropagationManager<C> {
       }
     }
 
+    if (!importingBlocks.add(block.getHash())) {
+      // We're already importing this block.
+      return CompletableFuture.completedFuture(block);
+    }
+
+    if (protocolContext.getBlockchain().contains(block.getHash())) {
+      // We've already imported this block.
+      importingBlocks.remove(block.getHash());
+      return CompletableFuture.completedFuture(block);
+    }
+
     // Import block
     final PersistBlockTask<C> importTask =
         PersistBlockTask.create(
@@ -256,8 +272,8 @@ public class BlockPropagationManager<C> {
         .scheduleSyncWorkerTask(importTask::run)
         .whenComplete(
             (r, t) -> {
+              importingBlocks.remove(block.getHash());
               if (t != null) {
-                // TODO do we time failures?  But we cannot drop a label in at this point.
                 LOG.warn(
                     "Failed to import announced block {} ({}).",
                     block.getHeader().getNumber(),
diff --git a/ethereum/eth/src/test/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManagerTest.java b/ethereum/eth/src/test/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManagerTest.java
index d72f8fb3b0..57d8e74bbf 100644
--- a/ethereum/eth/src/test/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManagerTest.java
+++ b/ethereum/eth/src/test/java/tech/pegasys/pantheon/ethereum/eth/sync/BlockPropagationManagerTest.java
@@ -14,9 +14,11 @@ package tech.pegasys.pantheon.ethereum.eth.sync;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 
 import tech.pegasys.pantheon.ethereum.ProtocolContext;
 import tech.pegasys.pantheon.ethereum.chain.Blockchain;
@@ -24,8 +26,12 @@ import tech.pegasys.pantheon.ethereum.chain.MutableBlockchain;
 import tech.pegasys.pantheon.ethereum.core.Block;
 import tech.pegasys.pantheon.ethereum.core.BlockDataGenerator;
 import tech.pegasys.pantheon.ethereum.core.BlockDataGenerator.BlockOptions;
+import tech.pegasys.pantheon.ethereum.eth.manager.EthContext;
+import tech.pegasys.pantheon.ethereum.eth.manager.EthMessages;
+import tech.pegasys.pantheon.ethereum.eth.manager.EthPeers;
 import tech.pegasys.pantheon.ethereum.eth.manager.EthProtocolManager;
 import tech.pegasys.pantheon.ethereum.eth.manager.EthProtocolManagerTestUtil;
+import tech.pegasys.pantheon.ethereum.eth.manager.EthScheduler;
 import tech.pegasys.pantheon.ethereum.eth.manager.RespondingEthPeer;
 import tech.pegasys.pantheon.ethereum.eth.manager.RespondingEthPeer.Responder;
 import tech.pegasys.pantheon.ethereum.eth.manager.ethtaskutils.BlockchainSetupUtil;
@@ -41,6 +47,8 @@ import tech.pegasys.pantheon.metrics.noop.NoOpMetricsSystem;
 import tech.pegasys.pantheon.util.uint.UInt256;
 
 import java.util.Collections;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Supplier;
 
 import org.junit.Before;
 import org.junit.BeforeClass;
@@ -530,4 +538,31 @@ public class BlockPropagationManagerTest {
     assertThat(peer.getEthPeer().chainState().getBestBlock().getTotalDifficulty())
         .isEqualTo(totalDifficulty);
   }
+
+  @SuppressWarnings("unchecked")
+  @Test
+  public void shouldNotImportBlocksThatAreAlreadyBeingImported() {
+    final EthScheduler ethScheduler = mock(EthScheduler.class);
+    when(ethScheduler.scheduleSyncWorkerTask(any(Supplier.class)))
+        .thenReturn(new CompletableFuture<>());
+    final EthContext ethContext =
+        new EthContext("eth", new EthPeers("eth"), new EthMessages(), ethScheduler);
+    final BlockPropagationManager<Void> blockPropagationManager =
+        new BlockPropagationManager<>(
+            syncConfig,
+            protocolSchedule,
+            protocolContext,
+            ethContext,
+            syncState,
+            pendingBlocks,
+            ethTasksTimer);
+
+    blockchainUtil.importFirstBlocks(2);
+    final Block nextBlock = blockchainUtil.getBlock(2);
+
+    blockPropagationManager.importOrSavePendingBlock(nextBlock);
+    blockPropagationManager.importOrSavePendingBlock(nextBlock);
+
+    verify(ethScheduler, times(1)).scheduleSyncWorkerTask(any(Supplier.class));
+  }
 }