diff --git a/eth/downloader/downloader_test.go b/eth/downloader/downloader_test.go
index 1b9f00c695..e18db00ed1 100644
--- a/eth/downloader/downloader_test.go
+++ b/eth/downloader/downloader_test.go
@@ -144,7 +144,12 @@ func (dl *downloadTester) HasFastBlock(hash common.Hash, number uint64) bool {
 func (dl *downloadTester) GetHeaderByHash(hash common.Hash) *types.Header {
 	dl.lock.RLock()
 	defer dl.lock.RUnlock()
+	return dl.getHeaderByHash(hash)
+}
 
+// getHeaderByHash returns the header if found either within ancients or own blocks)
+// This method assumes that the caller holds at least the read-lock (dl.lock)
+func (dl *downloadTester) getHeaderByHash(hash common.Hash) *types.Header {
 	header := dl.ancientHeaders[hash]
 	if header != nil {
 		return header
@@ -232,6 +237,13 @@ func (dl *downloadTester) GetTd(hash common.Hash, number uint64) *big.Int {
 	dl.lock.RLock()
 	defer dl.lock.RUnlock()
 
+	return dl.getTd(hash)
+}
+
+// getTd retrieves the block's total difficulty if found either within
+// ancients or own blocks).
+// This method assumes that the caller holds at least the read-lock (dl.lock)
+func (dl *downloadTester) getTd(hash common.Hash) *big.Int {
 	if td := dl.ancientChainTd[hash]; td != nil {
 		return td
 	}
@@ -243,8 +255,8 @@ func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq i
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
 	// Do a quick check, as the blockchain.InsertHeaderChain doesn't insert anything in case of errors
-	if _, ok := dl.ownHeaders[headers[0].ParentHash]; !ok {
-		return 0, errors.New("InsertHeaderChain: unknown parent at first position")
+	if dl.getHeaderByHash(headers[0].ParentHash) == nil {
+		return 0, fmt.Errorf("InsertHeaderChain: unknown parent at first position, parent of number %d", headers[0].Number)
 	}
 	var hashes []common.Hash
 	for i := 1; i < len(headers); i++ {
@@ -258,16 +270,18 @@ func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq i
 	// Do a full insert if pre-checks passed
 	for i, header := range headers {
 		hash := hashes[i]
-		if _, ok := dl.ownHeaders[hash]; ok {
+		if dl.getHeaderByHash(hash) != nil {
 			continue
 		}
-		if _, ok := dl.ownHeaders[header.ParentHash]; !ok {
+		if dl.getHeaderByHash(header.ParentHash) == nil {
 			// This _should_ be impossible, due to precheck and induction
 			return i, fmt.Errorf("InsertHeaderChain: unknown parent at position %d", i)
 		}
 		dl.ownHashes = append(dl.ownHashes, hash)
 		dl.ownHeaders[hash] = header
-		dl.ownChainTd[hash] = new(big.Int).Add(dl.ownChainTd[header.ParentHash], header.Difficulty)
+
+		td := dl.getTd(header.ParentHash)
+		dl.ownChainTd[hash] = new(big.Int).Add(td, header.Difficulty)
 	}
 	return len(headers), nil
 }
@@ -276,7 +290,6 @@ func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq i
 func (dl *downloadTester) InsertChain(blocks types.Blocks) (i int, err error) {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
-
 	for i, block := range blocks {
 		if parent, ok := dl.ownBlocks[block.ParentHash()]; !ok {
 			return i, fmt.Errorf("InsertChain: unknown parent at position %d / %d", i, len(blocks))
@@ -290,7 +303,9 @@ func (dl *downloadTester) InsertChain(blocks types.Blocks) (i int, err error) {
 		dl.ownBlocks[block.Hash()] = block
 		dl.ownReceipts[block.Hash()] = make(types.Receipts, 0)
 		dl.stateDb.Put(block.Root().Bytes(), []byte{0x00})
-		dl.ownChainTd[block.Hash()] = new(big.Int).Add(dl.ownChainTd[block.ParentHash()], block.Difficulty())
+
+		td := dl.getTd(block.ParentHash())
+		dl.ownChainTd[block.Hash()] = new(big.Int).Add(td, block.Difficulty())
 	}
 	return len(blocks), nil
 }
@@ -316,7 +331,6 @@ func (dl *downloadTester) InsertReceiptChain(blocks types.Blocks, receipts []typ
 			// Migrate from active db to ancient db
 			dl.ancientHeaders[blocks[i].Hash()] = blocks[i].Header()
 			dl.ancientChainTd[blocks[i].Hash()] = new(big.Int).Add(dl.ancientChainTd[blocks[i].ParentHash()], blocks[i].Difficulty())
-
 			delete(dl.ownHeaders, blocks[i].Hash())
 			delete(dl.ownChainTd, blocks[i].Hash())
 		} else {
diff --git a/miner/worker_test.go b/miner/worker_test.go
index 65eccbc4c0..a5c558ba5f 100644
--- a/miner/worker_test.go
+++ b/miner/worker_test.go
@@ -285,9 +285,7 @@ func testEmptyWork(t *testing.T, chainConfig *params.ChainConfig, engine consens
 	}
 	w.skipSealHook = func(task *task) bool { return true }
 	w.fullTaskHook = func() {
-		// Arch64 unit tests are running in a VM on travis, they must
-		// be given more time to execute.
-		time.Sleep(time.Second)
+		time.Sleep(100 * time.Millisecond)
 	}
 	w.start() // Start mining!
 	for i := 0; i < 2; i += 1 {