diff --git a/circle.yml b/circle.yml
index 653ab195c..4e2360354 100644
--- a/circle.yml
+++ b/circle.yml
@@ -1,14 +1,13 @@
 machine:
   node:
-    version: 5.1.0
-  environment:
-    SOURCE_MAP_SUPPORT: false
+    version: 6.0.0
 
 dependencies:
   pre:
     - cd /usr/local && sudo rm -rf go && curl https://storage.googleapis.com/golang/go1.6.2.linux-amd64.tar.gz | sudo tar -xz && sudo chmod a+w go/src/path/filepath
   post:
     - mv ./gopherjs $HOME/bin
+    - npm install --global source-map-support
     - npm install --global node-gyp
     - cd node-syscall && node-gyp rebuild && mkdir -p ~/.node_libraries/ && cp build/Release/syscall.node ~/.node_libraries/syscall.node
 
@@ -17,5 +16,5 @@ test:
     - diff -u <(echo -n) <(gofmt -d .)
     - go tool vet *.go                                                   # Go package in root directory.
     - for d in */; do echo $d; done | grep -v tests/ | grep -v third_party/ | xargs go tool vet # All subdirectories except "tests", "third_party".
-    - gopherjs test --short --minify github.com/gopherjs/gopherjs/tests github.com/gopherjs/gopherjs/tests/main github.com/gopherjs/gopherjs/js archive/tar archive/zip bufio bytes compress/bzip2 compress/flate compress/gzip compress/lzw compress/zlib container/heap container/list container/ring crypto/aes crypto/cipher crypto/des crypto/dsa crypto/ecdsa crypto/elliptic crypto/hmac crypto/md5 crypto/rand crypto/rc4 crypto/rsa crypto/sha1 crypto/sha256 crypto/sha512 crypto/subtle crypto/x509 database/sql database/sql/driver debug/dwarf debug/elf debug/macho debug/pe encoding/ascii85 encoding/asn1 encoding/base32 encoding/base64 encoding/binary encoding/csv encoding/gob encoding/hex encoding/json encoding/pem encoding/xml errors expvar flag fmt go/ast go/constant go/doc go/format go/parser go/printer go/scanner go/token hash/adler32 hash/crc32 hash/crc64 hash/fnv html html/template image image/color image/draw image/gif image/jpeg image/png index/suffixarray io io/ioutil math math/big math/cmplx math/rand mime mime/multipart mime/quotedprintable net/http/cookiejar net/http/fcgi net/mail net/rpc/jsonrpc net/textproto net/url path path/filepath reflect regexp regexp/syntax sort strconv strings sync sync/atomic testing/quick text/scanner text/tabwriter text/template text/template/parse time unicode unicode/utf16 unicode/utf8
-    - go test -v -race ./...
+    - NODE_PATH=$(npm root --global) gopherjs test --short --minify github.com/gopherjs/gopherjs/tests github.com/gopherjs/gopherjs/tests/main github.com/gopherjs/gopherjs/js archive/tar archive/zip bufio bytes compress/bzip2 compress/flate compress/gzip compress/lzw compress/zlib container/heap container/list container/ring crypto/aes crypto/cipher crypto/des crypto/dsa crypto/ecdsa crypto/elliptic crypto/hmac crypto/md5 crypto/rand crypto/rc4 crypto/rsa crypto/sha1 crypto/sha256 crypto/sha512 crypto/subtle crypto/x509 database/sql database/sql/driver debug/dwarf debug/elf debug/macho debug/pe encoding/ascii85 encoding/asn1 encoding/base32 encoding/base64 encoding/binary encoding/csv encoding/gob encoding/hex encoding/json encoding/pem encoding/xml errors expvar flag fmt go/ast go/constant go/doc go/format go/parser go/printer go/scanner go/token hash/adler32 hash/crc32 hash/crc64 hash/fnv html html/template image image/color image/draw image/gif image/jpeg image/png index/suffixarray io io/ioutil math math/big math/cmplx math/rand mime mime/multipart mime/quotedprintable net/http/cookiejar net/http/fcgi net/mail net/rpc/jsonrpc net/textproto net/url path path/filepath reflect regexp regexp/syntax sort strconv strings sync sync/atomic testing/quick text/scanner text/tabwriter text/template text/template/parse time unicode unicode/utf16 unicode/utf8
+    - NODE_PATH=$(npm root --global) go test -v -race ./...
diff --git a/tests/gorepo_test.go b/tests/gorepo_test.go
index 5496cd32e..1e9ac83e3 100644
--- a/tests/gorepo_test.go
+++ b/tests/gorepo_test.go
@@ -5,11 +5,19 @@ package tests_test
 import (
 	"os"
 	"os/exec"
+	"strconv"
 	"testing"
 )
 
 // Go repository basic compiler tests, and regression tests for fixed compiler bugs.
 func TestGoRepositoryCompilerTests(t *testing.T) {
+	if b, _ := strconv.ParseBool(os.Getenv("SOURCE_MAP_SUPPORT")); os.Getenv("SOURCE_MAP_SUPPORT") != "" && !b {
+		t.Fatal("Source maps disabled, but required for this test. Use SOURCE_MAP_SUPPORT=true or unset it completely.")
+	}
+	if err := exec.Command("node", "--require", "source-map-support/register", "--eval", "").Run(); err != nil {
+		t.Fatal("Source maps disabled, but required for this test. Use Node.js 4.x with source-map-support module for nice stack traces.")
+	}
+
 	args := []string{"go", "run", "run.go", "-summary"}
 	if testing.Verbose() {
 		args = append(args, "-v")
diff --git a/tests/run.go b/tests/run.go
index e90f06526..529464801 100644
--- a/tests/run.go
+++ b/tests/run.go
@@ -62,7 +62,6 @@ var knownFails = map[string]failReason{
 	"fixedbugs/issue4388.go":  {desc: "Error: expected <autogenerated>:1 have anonymous function:0"},
 	"fixedbugs/issue4562.go":  {desc: "Error: cannot find issue4562.go on stack"},
 	"fixedbugs/issue4620.go":  {desc: "map[0:1 1:2], Error: m[i] != 2"},
-	"fixedbugs/issue5856.go":  {desc: "BUG: defer called from /private/var/folders/tw/kgz4v2kn4n7d7ryg5k_z3dk40000gn/T/issue5856.go.931062983:15135, want issue5856.go:28"},
 	"fixedbugs/issue6899.go":  {desc: "incorrect output -0"},
 	"fixedbugs/issue7550.go":  {desc: "FATAL ERROR: invalid table size Allocation failed - process out of memory"},
 	"fixedbugs/issue7690.go":  {desc: "Error: runtime error: slice bounds out of range"},