diff --git a/.coveragerc b/.coveragerc
index f27b66a8..4d68b106 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -10,6 +10,7 @@ omit =
  test/tumbler-test.py
  test/test_tumbler.py
  test/test_donations.py
+ test/ygrunner.py
 
 [report]
 # Regexes for lines to exclude from consideration
diff --git a/cmttools/add-utxo.py b/cmttools/add-utxo.py
index 108bc664..30e119c5 100644
--- a/cmttools/add-utxo.py
+++ b/cmttools/add-utxo.py
@@ -19,7 +19,7 @@
 from optparse import OptionParser
 import bitcoin as btc
 from joinmarket import load_program_config, jm_single, get_p2pk_vbyte
-from joinmarket import Wallet
+from joinmarket import Wallet, sync_wallet
 from commitment_utils import get_utxo_info, validate_utxo_data, quit
 
 def add_external_commitments(utxo_datas):
@@ -144,6 +144,12 @@ def main():
         help='only validate the provided utxos (file or command line), not add',
         default=False
     )
+    parser.add_option('--fast',
+                      action='store_true',
+                      dest='fastsync',
+                      default=False,
+                      help=('choose to do fast wallet sync, only for Core and '
+                      'only for previously synced wallet'))
     (options, args) = parser.parse_args()
     load_program_config()
     utxo_data = []
@@ -172,7 +178,7 @@ def main():
                             options.maxmixdepth,
                             options.gaplimit)
         os.chdir(os.path.join(os.getcwd(), 'cmttools'))
-        jm_single().bc_interface.sync_wallet(wallet)
+        sync_wallet(wallet, fast=options.fastsync)
         unsp = {}
         for u, av in wallet.unspent.iteritems():
                     addr = av['address']
diff --git a/joinmarket/__init__.py b/joinmarket/__init__.py
index 23141091..23d92047 100644
--- a/joinmarket/__init__.py
+++ b/joinmarket/__init__.py
@@ -20,7 +20,7 @@
 from .configure import load_program_config, jm_single, get_p2pk_vbyte, \
     get_network, jm_single, get_network, validate_address, get_irc_mchannels, \
     check_utxo_blacklist
-from .blockchaininterface import BlockrInterface, BlockchainInterface
+from .blockchaininterface import BlockrInterface, BlockchainInterface, sync_wallet
 from .yieldgenerator import YieldGenerator, ygmain
 # Set default logging handler to avoid "No handler found" warnings.
 
diff --git a/joinmarket/blockchaininterface.py b/joinmarket/blockchaininterface.py
index a0d61d3d..3ad87f11 100644
--- a/joinmarket/blockchaininterface.py
+++ b/joinmarket/blockchaininterface.py
@@ -67,6 +67,16 @@ def is_index_ahead_of_cache(wallet, mix_depth, forchange):
     return wallet.index[mix_depth][forchange] >= wallet.index_cache[mix_depth][
         forchange]
 
+def sync_wallet(wallet, fast=False):
+    """Wrapper function to choose fast syncing where it's
+    both possible and requested.
+    """
+    if fast and (
+        isinstance(jm_single().bc_interface, BitcoinCoreInterface) or isinstance(
+                jm_single().bc_interface, RegtestBitcoinCoreInterface)):
+        jm_single().bc_interface.sync_wallet(wallet, fast=True)
+    else:
+        jm_single().bc_interface.sync_wallet(wallet)
 
 class BlockchainInterface(object):
     __metaclass__ = abc.ABCMeta
@@ -553,7 +563,7 @@ class BitcoinCoreInterface(BlockchainInterface):
     def __init__(self, jsonRpc, network):
         super(BitcoinCoreInterface, self).__init__()
         self.jsonRpc = jsonRpc
-
+        self.fast_sync_called = False
         blockchainInfo = self.jsonRpc.call("getblockchaininfo", [])
         actualNet = blockchainInfo['chain']
 
@@ -589,12 +599,79 @@ def add_watchonly_addresses(self, addr_list, wallet_name):
             print(' otherwise just restart this joinmarket script')
             sys.exit(0)
 
+    def sync_wallet(self, wallet, fast=False):
+        #trigger fast sync if the index_cache is available
+        #(and not specifically disabled).
+        if fast and wallet.index_cache != [[0,0]] * wallet.max_mix_depth:
+            self.sync_wallet_fast(wallet)
+            self.fast_sync_called = True
+            return
+        super(BitcoinCoreInterface, self).sync_wallet(wallet)
+        self.fast_sync_called = False
+
+    def sync_wallet_fast(self, wallet):
+        """Exploits the fact that given an index_cache,
+        all addresses necessary should be imported, so we
+        can just list all used addresses to find the right
+        index values.
+        """
+        self.get_address_usages(wallet)
+        self.sync_unspent(wallet)
+
+    def get_address_usages(self, wallet):
+        """Use rpc `listaddressgroupings` to locate all used
+        addresses in the account (whether spent or unspent outputs).
+        This will not result in a full sync if working with a new
+        Bitcoin Core instance, in which case "fast" should have been
+        specifically disabled by the user.
+        """
+        from joinmarket.wallet import BitcoinCoreWallet
+        if isinstance(wallet, BitcoinCoreWallet):
+            return
+        wallet_name = self.get_wallet_name(wallet)
+        agd = self.rpc('listaddressgroupings', [])
+        #flatten all groups into a single list; then, remove duplicates
+        fagd = [tuple(item) for sublist in agd for item in sublist]
+        #"deduplicated flattened address grouping data" = dfagd
+        dfagd = list(set(fagd))
+        #for lookup, want dict of form {"address": amount}
+        used_address_dict = {}
+        for addr_info in dfagd:
+            if len(addr_info) < 3 or addr_info[2] != wallet_name:
+                continue
+            used_address_dict[addr_info[0]] = (addr_info[1], addr_info[2])
+
+        log.debug("Fast sync in progress. Got this many used addresses: " + str(
+            len(used_address_dict)))
+        #Need to have wallet.index point to the last used address
+        #and fill addr_cache.
+        #For each branch:
+        #If index value is present, collect all addresses up to index+gap limit
+        #For each address in that list, mark used if seen in used_address_dict
+        used_indices = {}
+        for md in range(wallet.max_mix_depth):
+            used_indices[md] = {}
+            for fc in [0, 1]:
+                used_indices[md][fc] = []
+                for i in range(wallet.index_cache[md][fc]+wallet.gaplimit):
+                    if wallet.get_addr(md, fc, i) in used_address_dict.keys():
+                        used_indices[md][fc].append(i)
+                        wallet.addr_cache[wallet.get_addr(md, fc, i)] = (md, fc, i)
+                if len(used_indices[md][fc]):
+                    wallet.index[md][fc] = used_indices[md][fc][-1]
+                else:
+                    wallet.index[md][fc] = 0
+                if not is_index_ahead_of_cache(wallet, md, fc):
+                    wallet.index[md][fc] = wallet.index_cache[md][fc]
+        self.wallet_synced = True
+
+
     def sync_addresses(self, wallet):
         from joinmarket.wallet import BitcoinCoreWallet
 
         if isinstance(wallet, BitcoinCoreWallet):
             return
-        log.debug('requesting wallet history')
+        log.debug('requesting detailed wallet history')
         wallet_name = self.get_wallet_name(wallet)
         #TODO It is worth considering making this user configurable:
         addr_req_count = 20
diff --git a/joinmarket/yieldgenerator.py b/joinmarket/yieldgenerator.py
index cca4d002..222a0209 100644
--- a/joinmarket/yieldgenerator.py
+++ b/joinmarket/yieldgenerator.py
@@ -11,7 +11,7 @@
 from joinmarket import BlockrInterface
 from joinmarket import jm_single, get_network, load_program_config
 from joinmarket import get_log, calc_cj_fee, debug_dump_object
-from joinmarket import Wallet
+from joinmarket import Wallet, sync_wallet
 from joinmarket import get_irc_mchannels
 
 log = get_log()
@@ -102,6 +102,12 @@ def ygmain(ygclass, txfee=1000, cjfee_a=200, cjfee_r=0.002, ordertype='reloffer'
     parser.add_option('-g', '--gap-limit', action='store', type="int",
                       dest='gaplimit', default=6,
                       help='gap limit for wallet, default=6')
+    parser.add_option('--fast',
+                      action='store_true',
+                      dest='fastsync',
+                      default=False,
+                      help=('choose to do fast wallet sync, only for Core and '
+                      'only for previously synced wallet'))
     (options, args) = parser.parse_args()
     if len(args) < 1:
         parser.error('Needs a wallet')
@@ -142,7 +148,7 @@ def ygmain(ygclass, txfee=1000, cjfee_a=200, cjfee_r=0.002, ordertype='reloffer'
             return
 
     wallet = Wallet(seed, max_mix_depth=mix_levels, gaplimit=gaplimit)
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet, fast=options.fastsync)
 
     mcs = [IRCMessageChannel(c, realname='btcint=' + jm_single().config.get(
                                  "BLOCKCHAIN", "blockchain_source"),
diff --git a/patientsendpayment.py b/patientsendpayment.py
index a7f09ba4..f1ac5f8a 100644
--- a/patientsendpayment.py
+++ b/patientsendpayment.py
@@ -10,7 +10,7 @@
 from joinmarket import Maker, Taker, load_program_config, IRCMessageChannel
 from joinmarket import validate_address, jm_single
 from joinmarket import get_log, choose_orders, weighted_order_choose, \
-    debug_dump_object
+    debug_dump_object, sync_wallet
 from joinmarket import Wallet
 
 log = get_log()
@@ -194,6 +194,12 @@ def main():
             help=
             'Use the Bitcoin Core wallet through json rpc, instead of the internal joinmarket '
             + 'wallet. Requires blockchain_source=json-rpc')
+    parser.add_option('--fast',
+                      action='store_true',
+                      dest='fastsync',
+                      default=False,
+                      help=('choose to do fast wallet sync, only for Core and '
+                      'only for previously synced wallet'))
     (options, args) = parser.parse_args()
 
     if len(args) < 3:
@@ -221,7 +227,7 @@ def main():
         print 'not implemented yet'
         sys.exit(0)
     # wallet = BitcoinCoreWallet(fromaccount=wallet_name)
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet, fast=options.fastsync)
 
     available_balance = wallet.get_balance_by_mixdepth()[options.mixdepth]
     if available_balance < amount:
diff --git a/sendpayment.py b/sendpayment.py
index 497b6762..7e9dce81 100644
--- a/sendpayment.py
+++ b/sendpayment.py
@@ -15,7 +15,7 @@
 from joinmarket import validate_address, jm_single
 from joinmarket import get_log, choose_sweep_orders, choose_orders, \
     pick_order, cheapest_order_choose, weighted_order_choose, debug_dump_object
-from joinmarket import Wallet, BitcoinCoreWallet
+from joinmarket import Wallet, BitcoinCoreWallet, sync_wallet
 from joinmarket.wallet import estimate_tx_fee
 
 log = get_log()
@@ -276,6 +276,12 @@ def main():
         help=('Use the Bitcoin Core wallet through json rpc, instead '
               'of the internal joinmarket wallet. Requires '
               'blockchain_source=json-rpc'))
+    parser.add_option('--fast',
+                      action='store_true',
+                      dest='fastsync',
+                      default=False,
+                      help=('choose to do fast wallet sync, only for Core and '
+                      'only for previously synced wallet'))
     (options, args) = parser.parse_args()
 
     if len(args) < 3:
@@ -316,7 +322,7 @@ def main():
         wallet = Wallet(wallet_name, options.amtmixdepths, options.gaplimit)
     else:
         wallet = BitcoinCoreWallet(fromaccount=wallet_name)
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet, fast=options.fastsync)
 
     mcs = [IRCMessageChannel(c) for c in get_irc_mchannels()]
     mcc = MessageChannelCollection(mcs)
diff --git a/test/test_blockr.py b/test/test_blockr.py
index 41404f26..a9b3efd8 100644
--- a/test/test_blockr.py
+++ b/test/test_blockr.py
@@ -11,7 +11,7 @@
 
 import bitcoin as btc
 import pytest
-from joinmarket import load_program_config, jm_single
+from joinmarket import load_program_config, jm_single, sync_wallet
 from joinmarket.blockchaininterface import BlockrInterface
 from joinmarket import get_p2pk_vbyte, get_log, Wallet
 
@@ -62,7 +62,7 @@ def test_blockr_estimate_fee(setup_blockr):
 def test_blockr_sync(setup_blockr, net, seed, gaplimit, showprivkey, method):
     jm_single().config.set("BLOCKCHAIN", "network", net)
     wallet = Wallet(seed, max_mix_depth = 5)
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
 
     #copy pasted from wallet-tool; some boiled down form of
     #this should really be in wallet.py in the joinmarket module.
diff --git a/test/test_donations.py b/test/test_donations.py
index 95543e45..c827df90 100644
--- a/test/test_donations.py
+++ b/test/test_donations.py
@@ -10,7 +10,7 @@
 
 from commontest import make_wallets
 from joinmarket import load_program_config, get_p2pk_vbyte, get_log, jm_single
-from joinmarket import get_irc_mchannels, Taker
+from joinmarket import get_irc_mchannels, Taker, sync_wallet
 from joinmarket.configure import donation_address
 
 log = get_log()
@@ -24,7 +24,7 @@ def test_donation_address(setup_donations, amount):
     wallets = make_wallets(1, wallet_structures=[[1,1,1,0,0]],
                                mean_amt=0.5)
     wallet = wallets[0]['wallet']
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     #make a rdp from a simple privkey
     rdp_priv = "\x01"*32
     reusable_donation_pubkey = binascii.hexlify(secp256k1.PrivateKey(
diff --git a/test/test_podle.py b/test/test_podle.py
index 37ffa4c5..0a359cea 100644
--- a/test/test_podle.py
+++ b/test/test_podle.py
@@ -17,7 +17,7 @@
 from joinmarket import Taker, load_program_config, IRCMessageChannel
 from joinmarket import validate_address, jm_single, get_irc_mchannels
 from joinmarket import get_p2pk_vbyte, MessageChannelCollection
-from joinmarket import get_log, choose_sweep_orders, choose_orders, \
+from joinmarket import get_log, choose_sweep_orders, choose_orders, sync_wallet, \
     pick_order, cheapest_order_choose, weighted_order_choose, debug_dump_object
 import joinmarket.irc
 import sendpayment
@@ -145,7 +145,7 @@ def test_failed_sendpayment(setup_podle, num_ygs, wallet_structures, mean_amt,
 
     log.debug('starting sendpayment')
 
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     
     #Trigger PING LAG sending artificially
     joinmarket.irc.PING_INTERVAL = 3
@@ -241,7 +241,7 @@ def test_external_commitment_used(setup_podle):
 
     log.debug('starting sendpayment')
 
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     
     #Trigger PING LAG sending artificially
     joinmarket.irc.PING_INTERVAL = 3
@@ -347,7 +347,7 @@ def test_tx_commitments_used(setup_podle, consume_tx, age_required, cmt_age):
 
     log.debug('starting sendpayment')
 
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     log.debug("Here is the whole wallet: \n" + str(wallet.unspent))
     #Trigger PING LAG sending artificially
     joinmarket.irc.PING_INTERVAL = 3
diff --git a/test/test_regtest.py b/test/test_regtest.py
index 2af34950..641b3baa 100644
--- a/test/test_regtest.py
+++ b/test/test_regtest.py
@@ -10,7 +10,7 @@
 import pytest
 import time
 from joinmarket import (Taker, load_program_config, IRCMessageChannel,
-                        BitcoinCoreWallet)
+                        BitcoinCoreWallet, sync_wallet)
 from joinmarket import validate_address, jm_single, get_irc_mchannels
 from joinmarket import get_p2pk_vbyte, MessageChannelCollection
 from joinmarket import get_log, choose_sweep_orders, choose_orders, \
@@ -102,7 +102,7 @@ def test_sendpayment(setup_regtest, num_ygs, wallet_structures, mean_amt,
 
     log.debug('starting sendpayment')
 
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     
     #Trigger PING LAG sending artificially
     joinmarket.irc.PING_INTERVAL = 3
diff --git a/test/test_tumbler.py b/test/test_tumbler.py
index 9f26cc5c..0daf878e 100644
--- a/test/test_tumbler.py
+++ b/test/test_tumbler.py
@@ -11,7 +11,7 @@
 from joinmarket import Taker, load_program_config, IRCMessageChannel
 from joinmarket import validate_address, jm_single, MessageChannelCollection
 from joinmarket import get_p2pk_vbyte, get_irc_mchannels
-from joinmarket import get_log, choose_sweep_orders, choose_orders, \
+from joinmarket import get_log, choose_sweep_orders, choose_orders, sync_wallet, \
     pick_order, cheapest_order_choose, weighted_order_choose, debug_dump_object
 import json
 import tumbler
@@ -147,7 +147,7 @@ def test_tumbler(setup_tumbler, num_ygs, wallet_structures, mean_amt, sdev_amt,
 
     log.debug('starting tumbler')
 
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     jm_single().bc_interface.pushtx_failure_prob = 0.4
     mcs = [IRCMessageChannel(c) for c in get_irc_mchannels()]
     mcc = MessageChannelCollection(mcs)
diff --git a/test/test_tx_creation.py b/test/test_tx_creation.py
index 0e06a4ae..9f153659 100644
--- a/test/test_tx_creation.py
+++ b/test/test_tx_creation.py
@@ -15,7 +15,7 @@
 
 import bitcoin as btc
 import pytest
-from joinmarket import load_program_config, jm_single
+from joinmarket import load_program_config, jm_single, sync_wallet
 from joinmarket import get_p2pk_vbyte, get_log, Wallet
 from joinmarket.support import chunks, select_gradual, \
      select_greedy, select_greediest
@@ -41,7 +41,7 @@ def test_create_p2sh_output_tx(setup_tx_creation, nw, wallet_structures,
                                mean_amt, sdev_amt, amount, pubs, k):
     wallets = make_wallets(nw, wallet_structures, mean_amt, sdev_amt)
     for w in wallets.values():
-        jm_single().bc_interface.sync_wallet(w['wallet'])
+        sync_wallet(w['wallet'])
     for k, w in enumerate(wallets.values()):
         wallet = w['wallet']
         ins_full = wallet.select_utxos(0, amount)
@@ -65,7 +65,7 @@ def test_absurd_fees(setup_tx_creation):
     jm_single().bc_interface.absurd_fees = True
     #pay into it
     wallet = make_wallets(1, [[2, 0, 0, 0, 1]], 3)[0]['wallet']
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     amount = 350000000
     ins_full = wallet.select_utxos(0, amount)
     with pytest.raises(ValueError) as e_info:
@@ -76,7 +76,7 @@ def test_create_sighash_txs(setup_tx_creation):
     for sighash in [btc.SIGHASH_ANYONECANPAY + btc.SIGHASH_SINGLE,
                     btc.SIGHASH_NONE, btc.SIGHASH_SINGLE]:
         wallet = make_wallets(1, [[2, 0, 0, 0, 1]], 3)[0]['wallet']
-        jm_single().bc_interface.sync_wallet(wallet)
+        sync_wallet(wallet)
         amount = 350000000
         ins_full = wallet.select_utxos(0, amount)
         print "using hashcode: " + str(sighash)
@@ -105,7 +105,7 @@ def test_spend_p2sh_utxos(setup_tx_creation):
     msig_addr = btc.scriptaddr(script, magicbyte=196)
     #pay into it
     wallet = make_wallets(1, [[2, 0, 0, 0, 1]], 3)[0]['wallet']
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     amount = 350000000
     ins_full = wallet.select_utxos(0, amount)
     txid = make_sign_and_push(ins_full, wallet, amount, output_addr=msig_addr)
diff --git a/test/test_tx_notify.py b/test/test_tx_notify.py
index 30c7c954..79e386a9 100644
--- a/test/test_tx_notify.py
+++ b/test/test_tx_notify.py
@@ -9,7 +9,7 @@
 import bitcoin as btc
 import pytest
 from joinmarket import load_program_config, jm_single
-from joinmarket import get_log, Wallet
+from joinmarket import get_log, Wallet, sync_wallet
 
 log = get_log()
 
@@ -71,7 +71,7 @@ def make_tx_add_notify():
     amount = 250000000
     txfee = 10000
     wallet = wallet_dict['wallet']
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     inputs = wallet.select_utxos(0, amount)
     ins = inputs.keys()
     input_value = sum([i['value'] for i in inputs.values()])
diff --git a/test/test_wallets.py b/test/test_wallets.py
index 0045bedb..94561355 100644
--- a/test/test_wallets.py
+++ b/test/test_wallets.py
@@ -12,10 +12,11 @@
 import unittest
 from decimal import Decimal
 from commontest import local_command, interact, make_wallets, make_sign_and_push
+import json
 
 import bitcoin as btc
 import pytest
-from joinmarket import load_program_config, jm_single
+from joinmarket import load_program_config, jm_single, sync_wallet
 from joinmarket import get_p2pk_vbyte, get_log, Wallet
 from joinmarket.support import chunks, select_gradual, \
      select_greedy, select_greediest
@@ -36,42 +37,6 @@ def do_tx(wallet, amount):
     time.sleep(2) #blocks
     jm_single().bc_interface.sync_unspent(wallet)
 
-"""
-@pytest.mark.parametrize(
-    "num_txs, gap_count, gap_limit, wallet_structure, amount, wallet_file, password",
-    [
-        (3, 450, 461, [11,3,4,5,6], 150000000, 'test_import_wallet.json', 'import-pwd'
-         ),
-    ])
-def test_wallet_gap_sync(setup_wallets, num_txs, gap_count, gap_limit,
-                     wallet_structure, amount, wallet_file, password):
-    #Starting with a nonexistent index_cache, try syncing with a large
-    #gap limit
-    setup_import(mainnet=False)
-    wallet = make_wallets(1,[wallet_structure],
-                          fixed_seeds=[wallet_file],
-                          test_wallet=True, passwords=[password])[0]['wallet']
-    wallet.gaplimit = gap_limit
-    #Artificially insert coins at position (0, wallet_structures[0] + gap_count)
-    dest = wallet.get_addr(0, 0, wallet_structure[0] + gap_count)
-    btcamt = amount/(1e8)
-    jm_single().bc_interface.grab_coins(dest, amt=float(Decimal(btcamt).quantize(Decimal(10)**-8)))
-    time.sleep(2)
-    sync_count = 0
-    jm_single().bc_interface.wallet_synced = False
-    while not jm_single().bc_interface.wallet_synced:
-        wallet.index = []
-        for i in range(5):
-            wallet.index.append([0, 0])
-        jm_single().bc_interface.sync_wallet(wallet)
-        sync_count += 1
-        #avoid infinite loop
-        assert sync_count < 10
-        log.debug("Tried " + str(sync_count) + " times")
-
-    assert jm_single().bc_interface.wallet_synced
-"""
-
 @pytest.mark.parametrize(
     "num_txs, fake_count, wallet_structure, amount, wallet_file, password",
     [
@@ -90,7 +55,7 @@ def test_wallet_gap_sync(setup_wallets, num_txs, gap_count, gap_limit,
         #(25, 30, [30,20,1,1,1], 50000000, 'test_import_wallet.json', 'import-pwd'
         # ),
     ])
-def test_wallet_sync(setup_wallets, num_txs, fake_count,
+def test_wallet_sync_with_fast(setup_wallets, num_txs, fake_count,
                      wallet_structure, amount, wallet_file, password):
     setup_import(mainnet=False)
     wallet = make_wallets(1,[wallet_structure],
@@ -99,13 +64,14 @@ def test_wallet_sync(setup_wallets, num_txs, fake_count,
     sync_count = 0
     jm_single().bc_interface.wallet_synced = False
     while not jm_single().bc_interface.wallet_synced:
-        jm_single().bc_interface.sync_wallet(wallet)
+        sync_wallet(wallet)
         sync_count += 1
         #avoid infinite loop
         assert sync_count < 10
         log.debug("Tried " + str(sync_count) + " times")
 
     assert jm_single().bc_interface.wallet_synced
+    assert not jm_single().bc_interface.fast_sync_called
     #do some transactions with the wallet, then close, then resync
     for i in range(num_txs):
         do_tx(wallet, amount)
@@ -152,13 +118,13 @@ def test_wallet_sync(setup_wallets, num_txs, fake_count,
         #script over and over again)?
         sync_count += 1
         log.debug("TRYING SYNC NUMBER: " + str(sync_count))
-        jm_single().bc_interface.sync_wallet(wallet)
+        sync_wallet(wallet, fast=True)
+        assert jm_single().bc_interface.fast_sync_called
         #avoid infinite loop on failure.
         assert sync_count < 10
-    #Wallet should recognize index_cache on sync, so should not need to
-    #run sync process more than twice (twice if cache bump has moved us
-    #past the first round of imports).
-    assert sync_count <= 2
+    #Wallet should recognize index_cache on fast sync, so should not need to
+    #run sync process more than once.
+    assert sync_count == 1
     #validate the wallet index values after sync
     for i, ws in enumerate(wallet_structure):
         assert wallet.index[i][0] == ws #spends into external only
@@ -181,7 +147,7 @@ def test_wallet_sync(setup_wallets, num_txs, fake_count,
         # [(12,3),(100,99),(7, 40), (200, 201), (10,0)]
         # ),
         ([1,3,0,2,9], 'test_import_wallet.json', 'import-pwd',
-         [(0,7),(100,99),(0, 0), (200, 201), (21,41)]
+         [(1,7),(100,99),(0, 0), (200, 201), (21,41)]
          ),
     ])
 def test_wallet_sync_from_scratch(setup_wallets, wallet_structure,
@@ -202,13 +168,14 @@ def test_wallet_sync_from_scratch(setup_wallets, wallet_structure,
         wallet.index = []
         for i in range(5):
             wallet.index.append([0, 0])
-        jm_single().bc_interface.sync_wallet(wallet)
+        #will call with fast=False but index_cache exists; should use slow-sync
+        sync_wallet(wallet)
         sync_count += 1
         #avoid infinite loop
         assert sync_count < 10
         log.debug("Tried " + str(sync_count) + " times")
     #after #586 we expect to ALWAYS succeed within 2 rounds
-    assert sync_count == 2
+    assert sync_count <= 2
     #for each external branch, the new index may be higher than
     #the original index_cache if there was a higher used address
     expected_wallet_index = []
@@ -219,6 +186,8 @@ def test_wallet_sync_from_scratch(setup_wallets, wallet_structure,
             expected_wallet_index.append([wallet.index_cache[i][0],
                                           wallet.index_cache[i][1]])
     assert wallet.index == expected_wallet_index
+    log.debug("This is wallet unspent: ")
+    log.debug(json.dumps(wallet.unspent, indent=4))
 
 
 @pytest.mark.parametrize(
@@ -287,7 +256,7 @@ def test_utxo_selection(setup_wallets, nw, wallet_structures, mean_amt,
     wallets = make_wallets(nw, wallet_structures, mean_amt, sdev_amt)
     for w in wallets.values():
         jm_single().bc_interface.wallet_synced = False
-        jm_single().bc_interface.sync_wallet(w['wallet'])
+        sync_wallet(w['wallet'])
     for k, w in enumerate(wallets.values()):
         for algo in [select_gradual, select_greedy, select_greediest, None]:
             wallet = w['wallet']
diff --git a/test/ygrunner.py b/test/ygrunner.py
index c57dc4ab..308fb5cc 100644
--- a/test/ygrunner.py
+++ b/test/ygrunner.py
@@ -20,7 +20,7 @@
 import pytest
 import sys
 import time
-from joinmarket import load_program_config, jm_single
+from joinmarket import load_program_config, jm_single, sync_wallet
 
 #for running bots as subprocesses
 python_cmd = 'python2'
@@ -46,7 +46,7 @@ def test_start_ygs(setup_ygrunner, num_ygs, wallet_structures, mean_amt):
     wallet = wallets[num_ygs]['wallet']
     print "Seed : " + wallets[num_ygs]['seed']
     #useful to see the utxos on screen sometimes
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet)
     print wallet.unspent
 
     yigen_procs = []
diff --git a/tumbler.py b/tumbler.py
index 3b94f432..0654c3e4 100644
--- a/tumbler.py
+++ b/tumbler.py
@@ -13,7 +13,7 @@
 
 from joinmarket import jm_single, Taker, load_program_config, \
     IRCMessageChannel, MessageChannelCollection
-from joinmarket import validate_address
+from joinmarket import validate_address, sync_wallet
 from joinmarket import get_log, rand_norm_array, rand_pow_array, \
     rand_exp_array, choose_orders, weighted_order_choose, choose_sweep_orders, \
     debug_dump_object, get_irc_mchannels
@@ -545,6 +545,12 @@ def main():
             default=9,
             help=
             'maximum amount of times to re-create a transaction before giving up, default 9')
+    parser.add_option('--fast',
+                      action='store_true',
+                      dest='fastsync',
+                      default=False,
+                      help=('choose to do fast wallet sync, only for Core and '
+                      'only for previously synced wallet'))
     (options, args) = parser.parse_args()
     options = vars(options)
 
@@ -631,7 +637,7 @@ def main():
     # python tumbler.py -N 2 1 -c 3 0.001 -l 0.1 -M 3 -a 0 wallet_file 1xxx 1yyy
     wallet = Wallet(wallet_file,
                     max_mix_depth=options['mixdepthsrc'] + options['mixdepthcount'])
-    jm_single().bc_interface.sync_wallet(wallet)
+    sync_wallet(wallet, fast=options.fastsync)
     jm_single().wait_for_commitments = 1
     mcs = [IRCMessageChannel(c) for c in get_irc_mchannels()]
     mcc = MessageChannelCollection(mcs)
diff --git a/wallet-tool.py b/wallet-tool.py
index 03d50c68..d2617780 100644
--- a/wallet-tool.py
+++ b/wallet-tool.py
@@ -10,7 +10,7 @@
 
 from joinmarket import load_program_config, get_network, Wallet, encryptData, \
     get_p2pk_vbyte, jm_single, mn_decode, mn_encode, BitcoinCoreInterface, \
-    JsonRpcError
+    JsonRpcError, sync_wallet
 
 import bitcoin as btc
 
@@ -63,6 +63,12 @@
                   dest='csv',
                   default=False,
                   help=('When using the history method, output as csv'))
+parser.add_option('--fast',
+                  action='store_true',
+                  dest='fastsync',
+                  default=False,
+                  help=('choose to do fast wallet sync, only for Core and '
+                  'only for previously synced wallet'))
 (options, args) = parser.parse_args()
 
 # if the index_cache stored in wallet.json is longer than the default
@@ -104,7 +110,8 @@
         # unconfirmed balance is included in the wallet display by default
         if 'listunspent_args' not in jm_single().config.options('POLICY'):
             jm_single().config.set('POLICY','listunspent_args', '[0]')
-        jm_single().bc_interface.sync_wallet(wallet)
+
+        sync_wallet(wallet, fast=options.fastsync)
 
 if method == 'showutxos':
     unsp = {}