diff --git a/blockchain/chain.go b/blockchain/chain.go
index 00e2f3a6..0e48b694 100644
--- a/blockchain/chain.go
+++ b/blockchain/chain.go
@@ -1642,6 +1642,115 @@ func (b *BlockChain) LocateHeaders(locator BlockLocator, hashStop *chainhash.Has
 	return headers
 }
 
+// InvalidateBlock takes a block hash and invalidates it.
+//
+// This function is safe for concurrent access.
+func (b *BlockChain) InvalidateBlock(hash *chainhash.Hash) error {
+	return b.invalidateBlock(hash)
+}
+
+// invalidateBlock takes a block hash and invalidates it.
+func (b *BlockChain) invalidateBlock(hash *chainhash.Hash) error {
+	node := b.index.LookupNode(hash)
+	if node == nil {
+		err := fmt.Errorf("block %s is not known", hash)
+		return err
+	}
+
+	// No need to invalidate if its already invalid.
+	if node.status.KnownInvalid() {
+		err := fmt.Errorf("block %s is already invalid", hash)
+		return err
+	}
+
+	if node.parent == nil {
+		err := fmt.Errorf("block %s has no parent", hash)
+		return err
+	}
+
+	b.index.SetStatusFlags(node, statusValidateFailed)
+	b.index.UnsetStatusFlags(node, statusValid)
+
+	b.chainLock.Lock()
+	defer b.chainLock.Unlock()
+	detachNodes, attachNodes := b.getReorganizeNodes(node.parent)
+
+	err := b.reorganizeChain(detachNodes, attachNodes)
+	if err != nil {
+		return err
+	}
+
+	for i, e := 0, detachNodes.Front(); e != nil; i, e = i+1, e.Next() {
+		n := e.Value.(*blockNode)
+
+		b.index.SetStatusFlags(n, statusInvalidAncestor)
+		b.index.UnsetStatusFlags(n, statusValid)
+	}
+
+	if writeErr := b.index.flushToDB(); writeErr != nil {
+		log.Warnf("Error flushing block index changes to disk: %v", writeErr)
+	}
+
+	return nil
+}
+
+// ReconsiderBlock takes a block hash and allows it to be revalidated.
+//
+// This function is safe for concurrent access.
+func (b *BlockChain) ReconsiderBlock(hash *chainhash.Hash) error {
+	return b.reconsiderBlock(hash)
+}
+
+// reconsiderBlock takes a block hash and allows it to be revalidated.
+func (b *BlockChain) reconsiderBlock(hash *chainhash.Hash) error {
+	node := b.index.LookupNode(hash)
+	if node == nil {
+		err := fmt.Errorf("block %s is not known", hash)
+		return err
+	}
+
+	// No need to reconsider, it is already valid.
+	if node.status.KnownValid() {
+		err := fmt.Errorf("block %s is already valid", hash)
+		return err
+	}
+
+	// Keep a reference to the first node in the chain of invalid
+	// blocks so we can reprocess after status flags are updated.
+	firstNode := node
+
+	// Find previous node to the point where the blocks are valid again.
+	for n := node; n.status.KnownInvalid(); n = n.parent {
+		b.index.UnsetStatusFlags(n, statusInvalidAncestor)
+		b.index.UnsetStatusFlags(n, statusValidateFailed)
+
+		firstNode = n
+	}
+
+	var blk *btcutil.Block
+	err := b.db.View(func(dbTx database.Tx) error {
+		var err error
+		blk, err = dbFetchBlockByNode(dbTx, firstNode)
+		return err
+	})
+	if err != nil {
+		return err
+	}
+
+	// Process it all again. This will take care of the
+	// orphans as well.
+	_, _, err = b.ProcessBlock(blk, BFNoDupBlockCheck)
+	if err != nil {
+		return err
+	}
+
+	if writeErr := b.index.flushToDB(); writeErr != nil {
+		log.Warnf("Error flushing block index changes to disk: %v", writeErr)
+	}
+
+	return nil
+}
+
 // ClaimTrie returns the claimTrie associated wit hthe chain.
 func (b *BlockChain) ClaimTrie() *claimtrie.ClaimTrie {
 	return b.claimTrie
diff --git a/blockchain/process.go b/blockchain/process.go
index a48b6e50..8aaa91bc 100644
--- a/blockchain/process.go
+++ b/blockchain/process.go
@@ -29,6 +29,10 @@ const (
 	// not be performed.
 	BFNoPoWCheck
 
+	// BFNoDupBlockCheck signals if the block should skip existence
+	// checks.
+	BFNoDupBlockCheck
+
 	// BFNone is a convenience value to specifically indicate no flags.
 	BFNone BehaviorFlags = 0
 )
@@ -148,24 +152,26 @@ func (b *BlockChain) ProcessBlock(block *btcutil.Block, flags BehaviorFlags) (bo
 	blockHash := block.Hash()
 	log.Tracef("Processing block %v", blockHash)
 
-	// The block must not already exist in the main chain or side chains.
-	exists, err := b.blockExists(blockHash)
-	if err != nil {
-		return false, false, err
-	}
-	if exists {
-		str := fmt.Sprintf("already have block %v", blockHash)
-		return false, false, ruleError(ErrDuplicateBlock, str)
-	}
+	if flags&BFNoDupBlockCheck != BFNoDupBlockCheck {
+		// The block must not already exist in the main chain or side chains.
+		exists, err := b.blockExists(blockHash)
+		if err != nil {
+			return false, false, err
+		}
+		if exists {
+			str := fmt.Sprintf("already have block %v", blockHash)
+			return false, false, ruleError(ErrDuplicateBlock, str)
+		}
 
-	// The block must not already exist as an orphan.
-	if _, exists := b.orphans[*blockHash]; exists {
-		str := fmt.Sprintf("already have block (orphan) %v", blockHash)
-		return false, false, ruleError(ErrDuplicateBlock, str)
+		// The block must not already exist as an orphan.
+		if _, exists := b.orphans[*blockHash]; exists {
+			str := fmt.Sprintf("already have block (orphan) %v", blockHash)
+			return false, false, ruleError(ErrDuplicateBlock, str)
+		}
 	}
 
 	// Perform preliminary sanity checks on the block and its transactions.
-	err = checkBlockSanity(block, b.chainParams.PowLimit, b.timeSource, flags)
+	err := checkBlockSanity(block, b.chainParams.PowLimit, b.timeSource, flags)
 	if err != nil {
 		return false, false, err
 	}
diff --git a/rpcserver.go b/rpcserver.go
index 5c20436d..4797d64f 100644
--- a/rpcserver.go
+++ b/rpcserver.go
@@ -168,8 +168,10 @@ var rpcHandlersBeforeInit = map[string]commandHandler{
 	"getrawtransaction":      handleGetRawTransaction,
 	"gettxout":               handleGetTxOut,
 	"help":                   handleHelp,
+	"invalidateblock":        handleInvalidateBlock,
 	"node":                   handleNode,
 	"ping":                   handlePing,
+	"reconsiderblock":        handleReconsiderBlock,
 	"searchrawtransactions":  handleSearchRawTransactions,
 	"sendrawtransaction":     handleSendRawTransaction,
 	"setgenerate":            handleSetGenerate,
@@ -237,9 +239,7 @@ var rpcUnimplemented = map[string]struct{}{
 	"getchaintips":     {},
 	"getmempoolentry":  {},
 	"getwork":          {},
-	"invalidateblock":  {},
 	"preciousblock":    {},
-	"reconsiderblock":  {},
 }
 
 // Commands that are available to a limited user
@@ -2977,6 +2977,30 @@ func handleGetTxOut(s *rpcServer, cmd interface{}, closeChan <-chan struct{}) (i
 	return txOutReply, nil
 }
 
+// handleInvalidateBlock implements the invalidateblock command
+func handleInvalidateBlock(s *rpcServer, cmd interface{}, closeChan <-chan struct{}) (interface{}, error) {
+	c := cmd.(*btcjson.InvalidateBlockCmd)
+
+	hash, err := chainhash.NewHashFromStr(c.BlockHash)
+	if err != nil {
+		return nil, err
+	}
+
+	return nil, s.cfg.Chain.InvalidateBlock(hash)
+}
+
+// handleReconsiderBlock implements the reconsiderblock command
+func handleReconsiderBlock(s *rpcServer, cmd interface{}, closeChan <-chan struct{}) (interface{}, error) {
+	c := cmd.(*btcjson.ReconsiderBlockCmd)
+
+	hash, err := chainhash.NewHashFromStr(c.BlockHash)
+	if err != nil {
+		return nil, err
+	}
+
+	return nil, s.cfg.Chain.ReconsiderBlock(hash)
+}
+
 // handleHelp implements the help command.
 func handleHelp(s *rpcServer, cmd interface{}, closeChan <-chan struct{}) (interface{}, error) {
 	c := cmd.(*btcjson.HelpCmd)
diff --git a/rpcserverhelp.go b/rpcserverhelp.go
index a124e492..038b3495 100644
--- a/rpcserverhelp.go
+++ b/rpcserverhelp.go
@@ -568,10 +568,18 @@ var helpDescsEnUS = map[string]string{
 	"help--result0":    "List of commands",
 	"help--result1":    "Help for specified command",
 
+	// InvalidateBlockCmd
+	"invalidateblock--synopsis": "Invalidate a block.",
+	"invalidateblock-blockhash": "Hash of the block you want to invalidate",
+
 	// PingCmd help.
 	"ping--synopsis": "Queues a ping to be sent to each connected peer.\n" +
 		"Ping times are provided by getpeerinfo via the pingtime and pingwait fields.",
 
+	// ReconsiderBlockCmd
+	"reconsiderblock--synopsis": "Reconsider a block for validation.",
+	"reconsiderblock-blockhash": "Hash of the block you want to reconsider",
+
 	// SearchRawTransactionsCmd help.
 	"searchrawtransactions--synopsis": "Returns raw data for transactions involving the passed address.\n" +
 		"Returned transactions are pulled from both the database, and transactions currently in the mempool.\n" +
@@ -848,7 +856,9 @@ var rpcResultTypes = map[string][]interface{}{
 	"gettxout":               {(*btcjson.GetTxOutResult)(nil)},
 	"node":                   nil,
 	"help":                   {(*string)(nil), (*string)(nil)},
+	"invalidateblock":        nil,
 	"ping":                   nil,
+	"reconsiderblock":        nil,
 	"searchrawtransactions":  {(*string)(nil), (*[]btcjson.SearchRawTransactionsResult)(nil)},
 	"sendrawtransaction":     {(*string)(nil)},
 	"setgenerate":            nil,