diff --git a/core/vm/jit_test.go b/core/vm/jit_test.go
index 5e4bcfeef5..809abfea97 100644
--- a/core/vm/jit_test.go
+++ b/core/vm/jit_test.go
@@ -85,7 +85,7 @@ func TestCompiling(t *testing.T) {
 func TestResetInput(t *testing.T) {
 	var sender account
 
-	env := NewEnv(false, true)
+	env := NewEnv(&Config{EnableJit: true, ForceJit: true})
 	contract := NewContract(sender, sender, big.NewInt(100), big.NewInt(10000), big.NewInt(0))
 	contract.CodeAddr = &common.Address{}
 
@@ -144,7 +144,7 @@ func runVmBench(test vmBench, b *testing.B) {
 	if test.precompile && !test.forcejit {
 		NewProgram(test.code)
 	}
-	env := NewEnv(test.nojit, test.forcejit)
+	env := NewEnv(&Config{EnableJit: !test.nojit, ForceJit: test.forcejit})
 
 	b.ResetTimer()
 
@@ -166,12 +166,9 @@ type Env struct {
 	evm      *EVM
 }
 
-func NewEnv(noJit, forceJit bool) *Env {
+func NewEnv(config *Config) *Env {
 	env := &Env{gasLimit: big.NewInt(10000), depth: 0}
-	env.evm = New(env, Config{
-		EnableJit: !noJit,
-		ForceJit:  forceJit,
-	})
+	env.evm = New(env, *config)
 	return env
 }
 
diff --git a/core/vm/logger_test.go b/core/vm/logger_test.go
index a8c4cbc0b5..e85bca2277 100644
--- a/core/vm/logger_test.go
+++ b/core/vm/logger_test.go
@@ -47,7 +47,7 @@ type dummyEnv struct {
 
 func newDummyEnv(ref *dummyContractRef) *dummyEnv {
 	return &dummyEnv{
-		Env: NewEnv(true, false),
+		Env: NewEnv(&Config{EnableJit: false, ForceJit: false}),
 		ref: ref,
 	}
 }
@@ -57,7 +57,7 @@ func (d dummyEnv) GetAccount(common.Address) Account {
 
 func TestStoreCapture(t *testing.T) {
 	var (
-		env      = NewEnv(true, false)
+		env      = NewEnv(&Config{EnableJit: false, ForceJit: false})
 		logger   = NewStructLogger(nil)
 		mem      = NewMemory()
 		stack    = newstack()
diff --git a/eth/api.go b/eth/api.go
index a89b5162ec..f4bce47b84 100644
--- a/eth/api.go
+++ b/eth/api.go
@@ -25,6 +25,7 @@ import (
 	"math/big"
 	"os"
 	"runtime"
+	"time"
 
 	"github.com/ethereum/ethash"
 	"github.com/ethereum/go-ethereum/common"
@@ -38,8 +39,11 @@ import (
 	"github.com/ethereum/go-ethereum/miner"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/rpc"
+	"golang.org/x/net/context"
 )
 
+const defaultTraceTimeout = 5 * time.Second
+
 // PublicEthereumAPI provides an API to access Ethereum full node-related
 // information.
 type PublicEthereumAPI struct {
@@ -317,6 +321,13 @@ type BlockTraceResult struct {
 	Error      string                `json:"error"`
 }
 
+// TraceArgs holds extra parameters to trace functions
+type TraceArgs struct {
+	*vm.LogConfig
+	Tracer  *string
+	Timeout *string
+}
+
 // TraceBlock processes the given block's RLP but does not import the block in to
 // the chain.
 func (api *PrivateDebugAPI) TraceBlock(blockRlp []byte, config *vm.LogConfig) BlockTraceResult {
@@ -439,10 +450,42 @@ func formatError(err error) string {
 	return err.Error()
 }
 
+type timeoutError struct{}
+
+func (t *timeoutError) Error() string {
+	return "Execution time exceeded"
+}
+
 // TraceTransaction returns the structured logs created during the execution of EVM
 // and returns them as a JSON object.
-func (api *PrivateDebugAPI) TraceTransaction(txHash common.Hash, logConfig *vm.LogConfig) (*ethapi.ExecutionResult, error) {
-	logger := vm.NewStructLogger(logConfig)
+func (api *PrivateDebugAPI) TraceTransaction(ctx context.Context, txHash common.Hash, config *TraceArgs) (interface{}, error) {
+	var tracer vm.Tracer
+	if config != nil && config.Tracer != nil {
+		timeout := defaultTraceTimeout
+		if config.Timeout != nil {
+			var err error
+			if timeout, err = time.ParseDuration(*config.Timeout); err != nil {
+				return nil, err
+			}
+		}
+
+		var err error
+		if tracer, err = ethapi.NewJavascriptTracer(*config.Tracer); err != nil {
+			return nil, err
+		}
+
+		// Handle timeouts and RPC cancellations
+		deadlineCtx, cancel := context.WithTimeout(ctx, timeout)
+		go func() {
+			<-deadlineCtx.Done()
+			tracer.(*ethapi.JavascriptTracer).Stop(&timeoutError{})
+		}()
+		defer cancel()
+	} else if config == nil {
+		tracer = vm.NewStructLogger(nil)
+	} else {
+		tracer = vm.NewStructLogger(config.LogConfig)
+	}
 
 	// Retrieve the tx from the chain and the containing block
 	tx, blockHash, _, txIndex := core.GetTransaction(api.eth.ChainDb(), txHash)
@@ -488,16 +531,22 @@ func (api *PrivateDebugAPI) TraceTransaction(txHash common.Hash, logConfig *vm.L
 			continue
 		}
 		// Otherwise trace the transaction and return
-		vmenv := core.NewEnv(stateDb, api.config, api.eth.BlockChain(), msg, block.Header(), vm.Config{Debug: true, Tracer: logger})
+		vmenv := core.NewEnv(stateDb, api.config, api.eth.BlockChain(), msg, block.Header(), vm.Config{Debug: true, Tracer: tracer})
 		ret, gas, err := core.ApplyMessage(vmenv, msg, new(core.GasPool).AddGas(tx.Gas()))
 		if err != nil {
 			return nil, fmt.Errorf("tracing failed: %v", err)
 		}
-		return &ethapi.ExecutionResult{
-			Gas:         gas,
-			ReturnValue: fmt.Sprintf("%x", ret),
-			StructLogs:  ethapi.FormatLogs(logger.StructLogs()),
-		}, nil
+
+		switch tracer := tracer.(type) {
+		case *vm.StructLogger:
+			return &ethapi.ExecutionResult{
+				Gas:         gas,
+				ReturnValue: fmt.Sprintf("%x", ret),
+				StructLogs:  ethapi.FormatLogs(tracer.StructLogs()),
+			}, nil
+		case *ethapi.JavascriptTracer:
+			return tracer.GetResult()
+		}
 	}
 	return nil, errors.New("database inconsistency")
 }
diff --git a/internal/ethapi/tracer.go b/internal/ethapi/tracer.go
new file mode 100644
index 0000000000..27af1166b8
--- /dev/null
+++ b/internal/ethapi/tracer.go
@@ -0,0 +1,300 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethapi
+
+import (
+	"errors"
+	"fmt"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/robertkrimen/otto"
+)
+
+// fakeBig is used to provide an interface to Javascript for 'big.NewInt'
+type fakeBig struct{}
+
+// NewInt creates a new big.Int with the specified int64 value.
+func (fb *fakeBig) NewInt(x int64) *big.Int {
+	return big.NewInt(x)
+}
+
+// OpCodeWrapper provides a JavaScript-friendly wrapper around OpCode, to convince Otto to treat it
+// as an object, instead of a number.
+type opCodeWrapper struct {
+	op vm.OpCode
+}
+
+// toNumber returns the ID of this opcode as an integer
+func (ocw *opCodeWrapper) toNumber() int {
+	return int(ocw.op)
+}
+
+// toString returns the string representation of the opcode
+func (ocw *opCodeWrapper) toString() string {
+	return ocw.op.String()
+}
+
+// isPush returns true if the op is a Push
+func (ocw *opCodeWrapper) isPush() bool {
+	return ocw.op.IsPush()
+}
+
+// toValue returns an otto.Value for the opCodeWrapper
+func (ocw *opCodeWrapper) toValue(vm *otto.Otto) otto.Value {
+	value, _ := vm.ToValue(ocw)
+	obj := value.Object()
+	obj.Set("toNumber", ocw.toNumber)
+	obj.Set("toString", ocw.toString)
+	obj.Set("isPush", ocw.isPush)
+	return value
+}
+
+// memoryWrapper provides a JS wrapper around vm.Memory
+type memoryWrapper struct {
+	memory *vm.Memory
+}
+
+// slice returns the requested range of memory as a byte slice
+func (mw *memoryWrapper) slice(begin, end int64) []byte {
+	return mw.memory.Get(begin, end-begin)
+}
+
+// getUint returns the 32 bytes at the specified address interpreted
+// as an unsigned integer
+func (mw *memoryWrapper) getUint(addr int64) *big.Int {
+	ret := big.NewInt(0)
+	ret.SetBytes(mw.memory.GetPtr(addr, 32))
+	return ret
+}
+
+// toValue returns an otto.Value for the memoryWrapper
+func (mw *memoryWrapper) toValue(vm *otto.Otto) otto.Value {
+	value, _ := vm.ToValue(mw)
+	obj := value.Object()
+	obj.Set("slice", mw.slice)
+	obj.Set("getUint", mw.getUint)
+	return value
+}
+
+// stackWrapper provides a JS wrapper around vm.Stack
+type stackWrapper struct {
+	stack *vm.Stack
+}
+
+// peek returns the nth-from-the-top element of the stack.
+func (sw *stackWrapper) peek(idx int) *big.Int {
+	return sw.stack.Data()[len(sw.stack.Data())-idx-1]
+}
+
+// length returns the length of the stack
+func (sw *stackWrapper) length() int {
+	return len(sw.stack.Data())
+}
+
+// toValue returns an otto.Value for the stackWrapper
+func (sw *stackWrapper) toValue(vm *otto.Otto) otto.Value {
+	value, _ := vm.ToValue(sw)
+	obj := value.Object()
+	obj.Set("peek", sw.peek)
+	obj.Set("length", sw.length)
+	return value
+}
+
+// dbWrapper provides a JS wrapper around vm.Database
+type dbWrapper struct {
+	db vm.Database
+}
+
+// getBalance retrieves an account's balance
+func (dw *dbWrapper) getBalance(addr common.Address) *big.Int {
+	return dw.db.GetBalance(addr)
+}
+
+// getNonce retrieves an account's nonce
+func (dw *dbWrapper) getNonce(addr common.Address) uint64 {
+	return dw.db.GetNonce(addr)
+}
+
+// getCode retrieves an account's code
+func (dw *dbWrapper) getCode(addr common.Address) []byte {
+	return dw.db.GetCode(addr)
+}
+
+// getState retrieves an account's state data for the given hash
+func (dw *dbWrapper) getState(addr common.Address, hash common.Hash) common.Hash {
+	return dw.db.GetState(addr, hash)
+}
+
+// exists returns true iff the account exists
+func (dw *dbWrapper) exists(addr common.Address) bool {
+	return dw.db.Exist(addr)
+}
+
+// toValue returns an otto.Value for the dbWrapper
+func (dw *dbWrapper) toValue(vm *otto.Otto) otto.Value {
+	value, _ := vm.ToValue(dw)
+	obj := value.Object()
+	obj.Set("getBalance", dw.getBalance)
+	obj.Set("getNonce", dw.getNonce)
+	obj.Set("getCode", dw.getCode)
+	obj.Set("getState", dw.getState)
+	obj.Set("exists", dw.exists)
+	return value
+}
+
+// JavascriptTracer provides an implementation of Tracer that evaluates a
+// Javascript function for each VM execution step.
+type JavascriptTracer struct {
+	vm          *otto.Otto             // Javascript VM instance
+	traceobj    *otto.Object           // User-supplied object to call
+	log         map[string]interface{} // (Reusable) map for the `log` arg to `step`
+	logvalue    otto.Value             // JS view of `log`
+	opcode      *opCodeWrapper         // Wrapper around the opcode
+	opcodevalue otto.Value             // JS view of 'opcode'
+	memory      *memoryWrapper         // Wrapper around the VM memory
+	memvalue    otto.Value             // JS view of `memory`
+	stack       *stackWrapper          // Wrapper around the VM stack
+	stackvalue  otto.Value             // JS view of `stack`
+	db          *dbWrapper             // Wrapper around the VM environment
+	dbvalue     otto.Value             // JS view of `db`
+	err         error                  // Error, if one has occurred
+}
+
+// NewJavascriptTracer instantiates a new JavascriptTracer instance.
+// code specifies a Javascript snippet, which must evaluate to an expression
+// returning an object with 'step' and 'result' functions.
+func NewJavascriptTracer(code string) (*JavascriptTracer, error) {
+	vm := otto.New()
+	vm.Interrupt = make(chan func(), 1)
+
+	// Set up builtins for this environment
+	vm.Set("big", &fakeBig{})
+
+	jstracer, err := vm.Object("(" + code + ")")
+	if err != nil {
+		return nil, err
+	}
+
+	// Check the required functions exist
+	step, err := jstracer.Get("step")
+	if err != nil {
+		return nil, err
+	}
+	if !step.IsFunction() {
+		return nil, fmt.Errorf("Trace object must expose a function step()")
+	}
+
+	result, err := jstracer.Get("result")
+	if err != nil {
+		return nil, err
+	}
+	if !result.IsFunction() {
+		return nil, fmt.Errorf("Trace object must expose a function result()")
+	}
+
+	// Create the persistent log object
+	log := make(map[string]interface{})
+	logvalue, _ := vm.ToValue(log)
+
+	// Create persistent wrappers for memory and stack
+	opcode := &opCodeWrapper{}
+	mem := &memoryWrapper{}
+	stack := &stackWrapper{}
+	db := &dbWrapper{}
+
+	return &JavascriptTracer{
+		vm:          vm,
+		traceobj:    jstracer,
+		log:         log,
+		logvalue:    logvalue,
+		opcode:      opcode,
+		opcodevalue: opcode.toValue(vm),
+		memory:      mem,
+		memvalue:    mem.toValue(vm),
+		stack:       stack,
+		stackvalue:  stack.toValue(vm),
+		db:          db,
+		dbvalue:     db.toValue(vm),
+		err:         nil,
+	}, nil
+}
+
+// Stop terminates execution of any JavaScript
+func (jst *JavascriptTracer) Stop(err error) {
+	jst.vm.Interrupt <- func() {
+		panic(err)
+	}
+}
+
+// callSafely executes a method on a JS object, catching any panics and
+// returning them as error objects.
+func (jst *JavascriptTracer) callSafely(method string, argumentList ...interface{}) (ret interface{}, err error) {
+	defer func() {
+		if caught := recover(); caught != nil {
+			switch caught := caught.(type) {
+			case error:
+				err = caught
+			case string:
+				err = errors.New(caught)
+			case fmt.Stringer:
+				err = errors.New(caught.String())
+			default:
+				panic(caught)
+			}
+		}
+	}()
+
+	value, err := jst.traceobj.Call(method, argumentList...)
+	ret, _ = value.Export()
+	return ret, err
+}
+
+// CaptureState implements the Tracer interface to trace a single step of VM execution
+func (jst *JavascriptTracer) CaptureState(env vm.Environment, pc uint64, op vm.OpCode, gas, cost *big.Int, memory *vm.Memory, stack *vm.Stack, contract *vm.Contract, depth int, err error) {
+	if jst.err == nil {
+		jst.opcode.op = op
+		jst.memory.memory = memory
+		jst.stack.stack = stack
+		jst.db.db = env.Db()
+
+		jst.log["pc"] = pc
+		jst.log["op"] = jst.opcodevalue
+		jst.log["gas"] = gas.Int64()
+		jst.log["gasPrice"] = cost.Int64()
+		jst.log["memory"] = jst.memvalue
+		jst.log["stack"] = jst.stackvalue
+		jst.log["depth"] = depth
+		jst.log["account"] = contract.Address()
+		jst.log["err"] = err
+
+		_, err := jst.callSafely("step", jst.logvalue, jst.dbvalue)
+		if err != nil {
+			jst.err = err
+		}
+	}
+}
+
+// GetResult calls the Javascript 'result' function and returns its value, or any accumulated error
+func (jst *JavascriptTracer) GetResult() (result interface{}, err error) {
+	if jst.err != nil {
+		return nil, jst.err
+	}
+
+	return jst.callSafely("result")
+}
diff --git a/internal/ethapi/tracer_test.go b/internal/ethapi/tracer_test.go
new file mode 100644
index 0000000000..2f1dfa0bea
--- /dev/null
+++ b/internal/ethapi/tracer_test.go
@@ -0,0 +1,186 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethapi
+
+import (
+	"errors"
+	"math/big"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/crypto"
+)
+
+type ruleSet struct{}
+
+func (self *ruleSet) IsHomestead(*big.Int) bool { return true }
+
+type Env struct {
+	gasLimit *big.Int
+	depth    int
+	evm      *vm.EVM
+}
+
+func NewEnv(config *vm.Config) *Env {
+	env := &Env{gasLimit: big.NewInt(10000), depth: 0}
+	env.evm = vm.New(env, *config)
+	return env
+}
+
+func (self *Env) RuleSet() vm.RuleSet    { return &ruleSet{} }
+func (self *Env) Vm() vm.Vm              { return self.evm }
+func (self *Env) Origin() common.Address { return common.Address{} }
+func (self *Env) BlockNumber() *big.Int  { return big.NewInt(0) }
+
+//func (self *Env) PrevHash() []byte      { return self.parent }
+func (self *Env) Coinbase() common.Address  { return common.Address{} }
+func (self *Env) MakeSnapshot() vm.Database { return nil }
+func (self *Env) SetSnapshot(vm.Database)   {}
+func (self *Env) Time() *big.Int            { return big.NewInt(time.Now().Unix()) }
+func (self *Env) Difficulty() *big.Int      { return big.NewInt(0) }
+func (self *Env) Db() vm.Database           { return nil }
+func (self *Env) GasLimit() *big.Int        { return self.gasLimit }
+func (self *Env) VmType() vm.Type           { return vm.StdVmTy }
+func (self *Env) GetHash(n uint64) common.Hash {
+	return common.BytesToHash(crypto.Keccak256([]byte(big.NewInt(int64(n)).String())))
+}
+func (self *Env) AddLog(log *vm.Log) {
+}
+func (self *Env) Depth() int     { return self.depth }
+func (self *Env) SetDepth(i int) { self.depth = i }
+func (self *Env) CanTransfer(from common.Address, balance *big.Int) bool {
+	return true
+}
+func (self *Env) Transfer(from, to vm.Account, amount *big.Int) {}
+func (self *Env) Call(caller vm.ContractRef, addr common.Address, data []byte, gas, price, value *big.Int) ([]byte, error) {
+	return nil, nil
+}
+func (self *Env) CallCode(caller vm.ContractRef, addr common.Address, data []byte, gas, price, value *big.Int) ([]byte, error) {
+	return nil, nil
+}
+func (self *Env) Create(caller vm.ContractRef, data []byte, gas, price, value *big.Int) ([]byte, common.Address, error) {
+	return nil, common.Address{}, nil
+}
+func (self *Env) DelegateCall(me vm.ContractRef, addr common.Address, data []byte, gas, price *big.Int) ([]byte, error) {
+	return nil, nil
+}
+
+type account struct{}
+
+func (account) SubBalance(amount *big.Int)                          {}
+func (account) AddBalance(amount *big.Int)                          {}
+func (account) SetAddress(common.Address)                           {}
+func (account) Value() *big.Int                                     { return nil }
+func (account) SetBalance(*big.Int)                                 {}
+func (account) SetNonce(uint64)                                     {}
+func (account) Balance() *big.Int                                   { return nil }
+func (account) Address() common.Address                             { return common.Address{} }
+func (account) ReturnGas(*big.Int, *big.Int)                        {}
+func (account) SetCode([]byte)                                      {}
+func (account) ForEachStorage(cb func(key, value common.Hash) bool) {}
+
+func runTrace(tracer *JavascriptTracer) (interface{}, error) {
+	env := NewEnv(&vm.Config{Debug: true, Tracer: tracer})
+
+	contract := vm.NewContract(account{}, account{}, big.NewInt(0), env.GasLimit(), big.NewInt(1))
+	contract.Code = []byte{byte(vm.PUSH1), 0x1, byte(vm.PUSH1), 0x1, 0x0}
+
+	_, err := env.Vm().Run(contract, []byte{})
+	if err != nil {
+		return nil, err
+	}
+
+	return tracer.GetResult()
+}
+
+func TestTracing(t *testing.T) {
+	tracer, err := NewJavascriptTracer("{count: 0, step: function() { this.count += 1; }, result: function() { return this.count; }}")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ret, err := runTrace(tracer)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	value, ok := ret.(float64)
+	if !ok {
+		t.Errorf("Expected return value to be float64, was %T", ret)
+	}
+	if value != 3 {
+		t.Errorf("Expected return value to be 3, got %v", value)
+	}
+}
+
+func TestStack(t *testing.T) {
+	tracer, err := NewJavascriptTracer("{depths: [], step: function(log) { this.depths.push(log.stack.length()); }, result: function() { return this.depths; }}")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ret, err := runTrace(tracer)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	value, ok := ret.([]int)
+	if !ok {
+		t.Errorf("Expected return value to be []int, was %T", ret)
+	}
+	if len(value) != 3 || value[0] != 0 || value[1] != 1 || value[2] != 2 {
+		t.Errorf("Expected return value to be [0 1 2], got %v", value)
+	}
+}
+
+func TestHalt(t *testing.T) {
+	timeout := errors.New("stahp")
+	tracer, err := NewJavascriptTracer("{step: function() { while(1); }, result: function() { return null; }}")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	go func() {
+		time.Sleep(1 * time.Second)
+		tracer.Stop(timeout)
+	}()
+
+	if _, err = runTrace(tracer); err != timeout {
+		t.Errorf("Expected timeout error, got %v", err)
+	}
+}
+
+func TestHaltBetweenSteps(t *testing.T) {
+	tracer, err := NewJavascriptTracer("{step: function() {}, result: function() { return null; }}")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	env := NewEnv(&vm.Config{Debug: true, Tracer: tracer})
+	contract := vm.NewContract(&account{}, &account{}, big.NewInt(0), big.NewInt(0), big.NewInt(0))
+
+	tracer.CaptureState(env, 0, 0, big.NewInt(0), big.NewInt(0), nil, nil, contract, 0, nil)
+	timeout := errors.New("stahp")
+	tracer.Stop(timeout)
+	tracer.CaptureState(env, 0, 0, big.NewInt(0), big.NewInt(0), nil, nil, contract, 0, nil)
+
+	if _, err := tracer.GetResult(); err != timeout {
+		t.Errorf("Expected timeout error, got %v", err)
+	}
+}
diff --git a/internal/web3ext/web3ext.go b/internal/web3ext/web3ext.go
index e76e15177d..748b37c84a 100644
--- a/internal/web3ext/web3ext.go
+++ b/internal/web3ext/web3ext.go
@@ -284,7 +284,8 @@ web3._extend({
 		new web3._extend.Method({
 			name: 'traceTransaction',
 			call: 'debug_traceTransaction',
-			params: 1
+			params: 2,
+			inputFormatter: [null, null]
 		})
 	],
 	properties: []