diff --git a/lib/blockchain/chain.js b/lib/blockchain/chain.js
index 8bc94475..28173741 100644
--- a/lib/blockchain/chain.js
+++ b/lib/blockchain/chain.js
@@ -1136,6 +1136,21 @@ Chain.prototype._invalidate = co(function* _invalidate(hash) {
   this.chain.setInvalid(hash);
 });
 
+/**
+ * Retroactively prune the database.
+ * @method
+ * @returns {Promise}
+ */
+
+Chain.prototype.retroPrune = co(function* retroPrune() {
+  var unlock = yield this.locker.lock();
+  try {
+    return yield this.db.retroPrune(this.tip.hash);
+  } finally {
+    unlock();
+  }
+});
+
 /**
  * Scan the blockchain for transactions containing specified address hashes.
  * @method
@@ -2346,6 +2361,7 @@ function ChainOptions(options) {
   this.indexTX = false;
   this.indexAddress = false;
   this.forceWitness = false;
+  this.forcePrune = false;
 
   this.coinCache = 0;
   this.entryCache = 5000;
@@ -2430,6 +2446,13 @@ ChainOptions.prototype.fromOptions = function fromOptions(options) {
     this.forceWitness = options.forceWitness;
   }
 
+  if (options.forcePrune != null) {
+    assert(typeof options.forcePrune === 'boolean');
+    this.forcePrune = options.forcePrune;
+    if (options.forcePrune)
+      this.prune = true;
+  }
+
   if (options.coinCache != null) {
     assert(util.isNumber(options.coinCache));
     this.coinCache = options.coinCache;
diff --git a/lib/blockchain/chaindb.js b/lib/blockchain/chaindb.js
index 1245001f..ee68e6a2 100644
--- a/lib/blockchain/chaindb.js
+++ b/lib/blockchain/chaindb.js
@@ -91,7 +91,7 @@ ChainDB.prototype.open = co(function* open() {
 
   if (state) {
     // Verify options have not changed.
-    yield this.verifyFlags();
+    yield this.verifyFlags(state);
 
     // Verify deployment params have not changed.
     yield this.verifyDeployments();
@@ -492,18 +492,64 @@ ChainDB.prototype.getFlags = co(function* getFlags() {
 /**
  * Verify current options against db options.
  * @method
+ * @param {ChainState} state
  * @returns {Promise}
  */
 
-ChainDB.prototype.verifyFlags = co(function* verifyFlags() {
+ChainDB.prototype.verifyFlags = co(function* verifyFlags(state) {
+  var options = this.options;
   var flags = yield this.getFlags();
+  var needsWitness = false;
+  var needsPrune = false;
 
-  assert(flags, 'No flags found.');
+  if (!flags)
+    throw new Error('No flags found.');
 
-  flags.verify(this.options);
+  if (options.network !== flags.network)
+    throw new Error('Network mismatch for chain.');
 
-  if (this.options.forceWitness)
+  if (options.spv && !flags.spv)
+    throw new Error('Cannot retroactively enable SPV.');
+
+  if (!options.spv && flags.spv)
+    throw new Error('Cannot retroactively disable SPV.');
+
+  if (!flags.witness) {
+    if (!options.forceWitness)
+      throw new Error('Cannot retroactively enable witness.');
+    needsWitness = true;
+  }
+
+  if (options.prune && !flags.prune) {
+    if (!options.forcePrune)
+      throw new Error('Cannot retroactively prune.');
+    needsPrune = true;
+  }
+
+  if (!options.prune && flags.prune)
+    throw new Error('Cannot retroactively unprune.');
+
+  if (options.indexTX && !flags.indexTX)
+    throw new Error('Cannot retroactively enable TX indexing.');
+
+  if (!options.indexTX && flags.indexTX)
+    throw new Error('Cannot retroactively disable TX indexing.');
+
+  if (options.indexAddress && !flags.indexAddress)
+    throw new Error('Cannot retroactively enable address indexing.');
+
+  if (!options.indexAddress && flags.indexAddress)
+    throw new Error('Cannot retroactively disable address indexing.');
+
+  if (needsWitness) {
+    yield this.logger.info('Writing witness bit to chain flags.');
     yield this.saveFlags();
+  }
+
+  if (needsPrune) {
+    yield this.logger.info('Retroactively pruning chain.');
+    yield this.retroPrune(state.hash());
+  }
 });
 
 /**
@@ -653,6 +699,58 @@ ChainDB.prototype.invalidateCache = co(function* invalidateCache(bit, batch) {
   }
 });
 
+/**
+ * Retroactively prune the database.
+ * @method
+ * @param {Hash} tip
+ * @returns {Promise}
+ */
+
+ChainDB.prototype.retroPrune = co(function* retroPrune(tip) {
+  var options = this.options;
+  var keepBlocks = this.network.block.keepBlocks;
+  var pruneAfter = this.network.block.pruneAfterHeight;
+  var flags = yield this.getFlags();
+  var height = yield this.getHeight(tip);
+  var i, start, end, batch, hash;
+
+  if (flags.prune)
+    throw new Error('Already pruned.');
+
+  if (height <= pruneAfter + keepBlocks)
+    return false;
+
+  batch = this.db.batch();
+  start = pruneAfter + 1;
+  end = height - keepBlocks;
+
+  for (i = start; i <= end; i++) {
+    hash = yield this.getHash(i);
+
+    if (!hash)
+      throw new Error('Cannot find hash for ' + i);
+
+    batch.del(layout.b(hash));
+    batch.del(layout.u(hash));
+  }
+
+  try {
+    options.prune = true;
+
+    flags = ChainFlags.fromOptions(options);
+    assert(flags.prune);
+
+    batch.put(layout.O, flags.toRaw());
+
+    yield batch.write();
+  } catch (e) {
+    options.prune = false;
+    throw e;
+  }
+
+  return true;
+});
+
 /**
  * Get the _next_ block hash (does not work by height).
  * @method
@@ -1946,40 +2044,6 @@ ChainFlags.fromOptions = function fromOptions(data) {
   return new ChainFlags().fromOptions(data);
 };
 
-ChainFlags.prototype.verify = function verify(options) {
-  if (options.network !== this.network)
-    throw new Error('Network mismatch for chain.');
-
-  if (options.spv && !this.spv)
-    throw new Error('Cannot retroactively enable SPV.');
-
-  if (!options.spv && this.spv)
-    throw new Error('Cannot retroactively disable SPV.');
-
-  if (!options.forceWitness) {
-    if (!this.witness)
-      throw new Error('Cannot retroactively enable witness.');
-  }
-
-  if (options.prune && !this.prune)
-    throw new Error('Cannot retroactively prune.');
-
-  if (!options.prune && this.prune)
-    throw new Error('Cannot retroactively unprune.');
-
-  if (options.indexTX && !this.indexTX)
-    throw new Error('Cannot retroactively enable TX indexing.');
-
-  if (!options.indexTX && this.indexTX)
-    throw new Error('Cannot retroactively disable TX indexing.');
-
-  if (options.indexAddress && !this.indexAddress)
-    throw new Error('Cannot retroactively enable address indexing.');
-
-  if (!options.indexAddress && this.indexAddress)
-    throw new Error('Cannot retroactively disable address indexing.');
-};
-
 ChainFlags.prototype.toRaw = function toRaw() {
   var bw = new StaticWriter(12);
   var flags = 0;
diff --git a/lib/http/rpc.js b/lib/http/rpc.js
index 19ec3563..298d90bb 100644
--- a/lib/http/rpc.js
+++ b/lib/http/rpc.js
@@ -94,6 +94,7 @@ RPC.prototype.init = function init() {
   this.add('getrawmempool', this.getRawMempool);
   this.add('gettxout', this.getTXOut);
   this.add('gettxoutsetinfo', this.getTXOutSetInfo);
+  this.add('pruneblockchain', this.pruneBlockchain);
   this.add('verifychain', this.verifyChain);
 
   this.add('invalidateblock', this.invalidateBlock);
@@ -459,7 +460,12 @@ RPC.prototype.setBan = co(function* setBan(args, help) {
       'setban "ip(/netmask)" "add|remove" (bantime) (absolute)');
   }
 
-  addr = NetAddress.fromHostname(addr, this.network);
+  try {
+    addr = NetAddress.fromHostname(addr, this.network);
+  } catch (e) {
+    throw new RPCError(errs.CLIENT_INVALID_IP_OR_SUBNET,
+      'Invalid IP or subnet.');
+  }
 
   switch (action) {
     case 'add':
@@ -571,7 +577,7 @@ RPC.prototype.getBlock = co(function* getBlock(args, help) {
     if (this.chain.options.prune)
       throw new RPCError(errs.MISC_ERROR, 'Block not available (pruned data)');
 
-    throw new RPCError(errs.DATABASE_ERROR, 'Can\'t read block from disk');
+    throw new RPCError(errs.MISC_ERROR, 'Can\'t read block from disk');
   }
 
   if (!verbose)
@@ -997,6 +1003,26 @@ RPC.prototype.getTXOutSetInfo = co(function* getTXOutSetInfo(args, help) {
   };
 });
 
+RPC.prototype.pruneBlockchain = co(function* pruneBlockchain(args, help) {
+  if (help || args.length !== 0)
+    throw new RPCError(errs.MISC_ERROR, 'pruneblockchain');
+
+  if (this.chain.options.spv)
+    throw new RPCError(errs.MISC_ERROR, 'Cannot prune chain in SPV mode.');
+
+  if (this.chain.options.prune)
+    throw new RPCError(errs.MISC_ERROR, 'Chain is already pruned.');
+
+  if (this.chain.height < this.network.block.pruneAfterHeight)
+    throw new RPCError(errs.MISC_ERROR, 'Chain is too short for pruning.');
+
+  try {
+    yield this.chain.retroPrune();
+  } catch (e) {
+    throw new RPCError(errs.DATABASE_ERROR, e.message);
+  }
+});
+
 RPC.prototype.verifyChain = co(function* verifyChain(args, help) {
   var valid = new Validator([args]);
   var level = valid.u32(0);
diff --git a/lib/node/fullnode.js b/lib/node/fullnode.js
index 4905c294..d80ff4ba 100644
--- a/lib/node/fullnode.js
+++ b/lib/node/fullnode.js
@@ -57,6 +57,7 @@ function FullNode(options) {
     maxFiles: this.config.num('max-files'),
     cacheSize: this.config.mb('cache-size'),
     forceWitness: this.config.bool('force-witness'),
+    forcePrune: this.config.bool('force-prune'),
     prune: this.config.bool('prune'),
     checkpoints: this.config.bool('checkpoints'),
     coinCache: this.config.mb('coin-cache'),