diff --git a/.travis.yml b/.travis.yml
index 7e6e53fa..7f0c7112 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,10 @@ language: go
 os:
   - linux
   - osx
+before_script:
+  - rvm get head || true # https://github.com/travis-ci/travis-ci/issues/6307 
+  - set -e
 # Run gofmt and lint serially to avoid confusing output. Run tests in parallel
 # for speed.
 script: make gofmt lint && make -j2 test
+after_script: set +e
diff --git a/Makefile b/Makefile
index c320a98a..9398f9e7 100644
--- a/Makefile
+++ b/Makefile
@@ -33,7 +33,7 @@ endif
 PYTHON_BIN := $(shell which $(PYTHON))
 PYTHON_VER := $(word 2,$(shell $(PYTHON) -V 2>&1))
 GO_REQ_MAJ := 1
-GO_REQ_MIN := 6
+GO_REQ_MIN := 9
 GO_MAJ_MIN := $(subst go,, $(word 3,$(shell go version 2>&1)) )
 GO_MAJ := $(word 1,$(subst ., ,$(GO_MAJ_MIN) ))
 GO_MIN := $(word 2,$(subst ., ,$(GO_MAJ_MIN) ))
diff --git a/runtime/complex.go b/runtime/complex.go
index c5ca7c92..752ca4c5 100644
--- a/runtime/complex.go
+++ b/runtime/complex.go
@@ -457,7 +457,7 @@ func complexModOp(v, w complex128) complex128 {
 }
 
 const (
-	_ = iota
+	blank = iota
 	real1
 	imag1
 	real2
diff --git a/runtime/complex_test.go b/runtime/complex_test.go
index 2001e48f..61b68722 100644
--- a/runtime/complex_test.go
+++ b/runtime/complex_test.go
@@ -75,6 +75,10 @@ func TestComplexEq(t *testing.T) {
 	}
 }
 
+// FIXME(corona10): Since Go 1.9 moved to C99 float division and what CPython uses as well.
+// Some tests can be failed with version < Go 1.9. We need to detect Go version.
+// And changed expected values.
+
 func TestComplexBinaryOps(t *testing.T) {
 	cases := []struct {
 		fun     func(f *Frame, v, w *Object) (*Object, *BaseException)
@@ -107,8 +111,8 @@ func TestComplexBinaryOps(t *testing.T) {
 		{Div, NewComplex(3 - 4i).ToObject(), NewLong(big.NewInt(-34)).ToObject(), NewComplex(-0.08823529411764706 + 0.11764705882352941i).ToObject(), nil},
 		{Div, NewComplex(3 + 4i).ToObject(), NewComplex(complex(math.Inf(1), math.Inf(-1))).ToObject(), NewComplex(0i).ToObject(), nil},
 		{Div, NewComplex(3 + 4i).ToObject(), NewComplex(complex(math.Inf(1), 2)).ToObject(), NewComplex(0i).ToObject(), nil},
-		{Div, NewComplex(complex(math.Inf(1), math.Inf(1))).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.Inf(1), math.Inf(1))).ToObject(), nil},
-		{Div, NewComplex(complex(math.Inf(1), 4)).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.Inf(1), math.Inf(1))).ToObject(), nil},
+		{Div, NewComplex(complex(math.Inf(1), math.Inf(1))).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.Inf(1), math.NaN())).ToObject(), nil},
+		{Div, NewComplex(complex(math.Inf(1), 4)).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.Inf(1), math.Inf(-1))).ToObject(), nil},
 		{Div, NewComplex(complex(3, math.Inf(1))).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.Inf(1), math.Inf(1))).ToObject(), nil},
 		{Div, NewComplex(complex(3, math.NaN())).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.NaN(), math.NaN())).ToObject(), nil},
 		{Div, NewStr("foo").ToObject(), NewComplex(1 + 2i).ToObject(), nil, mustCreateException(TypeErrorType, "unsupported operand type(s) for /: 'str' and 'complex'")},
@@ -189,8 +193,8 @@ func TestComplexBinaryOps(t *testing.T) {
 		{Pow, NewComplex(complex(math.Inf(-1), 2)).ToObject(), NewComplex(1 + 2i).ToObject(), NewComplex(complex(math.NaN(), math.NaN())).ToObject(), nil},
 		{Pow, NewComplex(1 + 2i).ToObject(), NewComplex(complex(1, math.Inf(1))).ToObject(), NewComplex(complex(math.NaN(), math.NaN())).ToObject(), nil},
 		{Pow, NewComplex(complex(math.NaN(), 1)).ToObject(), NewComplex(3 + 4i).ToObject(), NewComplex(complex(math.NaN(), math.NaN())).ToObject(), nil},
-		{Pow, NewComplex(3 + 4i).ToObject(), NewInt(3).ToObject(), NewComplex(-117 + 44.000000000000036i).ToObject(), nil},
-		{Pow, NewComplex(3 + 4i).ToObject(), NewFloat(3.1415).ToObject(), NewComplex(-152.8892667678244 + 35.55533513049651i).ToObject(), nil},
+		{Pow, NewComplex(3 + 4i).ToObject(), NewInt(3).ToObject(), NewComplex(-117 + 44.00000000000003i).ToObject(), nil},
+		{Pow, NewComplex(3 + 4i).ToObject(), NewFloat(3.1415).ToObject(), NewComplex(-152.8892667678244 + 35.555335130496516i).ToObject(), nil},
 		{Pow, NewComplex(3 + 4i).ToObject(), NewLong(big.NewInt(123)).ToObject(), NewComplex(5.393538720276193e+85 + 7.703512580443326e+85i).ToObject(), nil},
 		{Pow, NewComplex(1 + 2i).ToObject(), NewStr("foo").ToObject(), nil, mustCreateException(TypeErrorType, "unsupported operand type(s) for **: 'complex' and 'str'")},
 		{Pow, NewStr("foo").ToObject(), NewComplex(1 + 2i).ToObject(), nil, mustCreateException(TypeErrorType, "unsupported operand type(s) for **: 'str' and 'complex'")},
diff --git a/runtime/dict.go b/runtime/dict.go
index 66a07e67..32eeca43 100644
--- a/runtime/dict.go
+++ b/runtime/dict.go
@@ -230,7 +230,7 @@ func (iter *dictEntryIterator) next() *dictEntry {
 		// 64bit atomic ops need to be 8 byte aligned. This compile time check
 		// verifies alignment by creating a negative constant for an unsigned type.
 		// See sync/atomic docs for details.
-		const _ = -(unsafe.Offsetof(iter.index) % 8)
+		const blank = -(unsafe.Offsetof(iter.index) % 8)
 		index := int(atomic.AddInt64(&iter.index, 1)) - 1
 		if index >= numEntries {
 			break
@@ -310,7 +310,7 @@ func (d *Dict) loadVersion() int64 {
 	// 64bit atomic ops need to be 8 byte aligned. This compile time check
 	// verifies alignment by creating a negative constant for an unsigned type.
 	// See sync/atomic docs for details.
-	const _ = -(unsafe.Offsetof(d.version) % 8)
+	const blank = -(unsafe.Offsetof(d.version) % 8)
 	return atomic.LoadInt64(&d.version)
 }
 
@@ -319,7 +319,7 @@ func (d *Dict) incVersion() {
 	// 64bit atomic ops need to be 8 byte aligned. This compile time check
 	// verifies alignment by creating a negative constant for an unsigned type.
 	// See sync/atomic docs for details.
-	const _ = -(unsafe.Offsetof(d.version) % 8)
+	const blank = -(unsafe.Offsetof(d.version) % 8)
 	atomic.AddInt64(&d.version, 1)
 }
 
diff --git a/runtime/file_test.go b/runtime/file_test.go
index 2e04ea7c..d292408d 100644
--- a/runtime/file_test.go
+++ b/runtime/file_test.go
@@ -73,7 +73,7 @@ func TestFileCloseExit(t *testing.T) {
 		cases := []invokeTestCase{
 			{args: wrapArgs(newObject(FileType)), want: None},
 			{args: wrapArgs(f.open("r")), want: None},
-			{args: wrapArgs(closedFile), wantExc: mustCreateException(IOErrorType, "invalid argument")},
+			{args: wrapArgs(closedFile), wantExc: mustCreateException(IOErrorType, closedFile.file.Close().Error())},
 		}
 		for _, cas := range cases {
 			if err := runInvokeMethodTestCase(FileType, method, &cas); err != "" {
diff --git a/runtime/set.go b/runtime/set.go
index a19897a7..54aa2914 100644
--- a/runtime/set.go
+++ b/runtime/set.go
@@ -106,10 +106,7 @@ func (s *Set) ToObject() *Object {
 // Update inserts all elements in the iterable o into s.
 func (s *Set) Update(f *Frame, o *Object) *BaseException {
 	raised := seqForEach(f, o, func(key *Object) *BaseException {
-		if raised := s.dict.SetItem(f, key, None); raised != nil {
-			return raised
-		}
-		return nil
+		return s.dict.SetItem(f, key, None)
 	})
 	return raised
 }