diff --git a/ast.go b/ast.go
index 084cc36d..444fd554 100644
--- a/ast.go
+++ b/ast.go
@@ -175,6 +175,20 @@ func toBasicType(pkg *Package, t *types.Basic) ast.Expr {
 	return &ast.Ident{Name: t.Name()}
 }
 
+func isBasicUntyped(typ types.Type) bool {
+	if t, ok := typ.(*types.Basic); ok {
+		return (t.Info() & types.IsUntyped) != 0
+	}
+	return false
+}
+
+func isBasicUntypedKind(typ types.Type) (bool, types.BasicKind) {
+	if t, ok := typ.(*types.Basic); ok {
+		return (t.Info() & types.IsUntyped) != 0, t.Kind()
+	}
+	return false, types.Invalid
+}
+
 func isUntyped(pkg *Package, typ types.Type) bool {
 	switch t := typ.(type) {
 	case *types.Basic:
@@ -682,6 +696,7 @@ retry:
 			cval = unaryOp(pkg, t.tok(), args)
 		} else if t.isOp() {
 			cval = binaryOp(&pkg.cb, t.tok(), args)
+			pkg.cb.recordUpdateUntypedBinaryOp(t.tok(), args, nil)
 		} else if t.hasApproxType() {
 			flags |= instrFlagApproxType
 		}
@@ -707,6 +722,7 @@ retry:
 	switch t := fn.Val.(type) {
 	case *ast.BinaryExpr:
 		t.X, t.Y = checkParenExpr(args[0].Val), checkParenExpr(args[1].Val)
+		pkg.cb.recordUpdateUntypedBinaryOp(t.Op, args, tyRet)
 		return &internal.Elem{Val: t, Type: tyRet, CVal: cval}, nil
 	case *ast.UnaryExpr:
 		t.X = args[0].Val
@@ -734,6 +750,7 @@ func matchTypeCast(pkg *Package, typ types.Type, fn *internal.Elem, args []*inte
 		fnVal = &ast.ParenExpr{X: fnVal}
 	}
 	if len(args) == 1 && ConvertibleTo(pkg, args[0].Type, typ) {
+		pkg.cb.recordUpdateUntyped(args[0], typ)
 		if args[0].CVal != nil {
 			if t, ok := typ.(*types.Named); ok {
 				o := t.Obj()
@@ -1020,9 +1037,11 @@ func matchFuncType(
 func matchFuncArgs(
 	pkg *Package, args []*internal.Elem, sig *types.Signature, at interface{}) error {
 	for i, arg := range args {
-		if err := matchType(pkg, arg, getParam(sig, i).Type(), at); err != nil {
+		typ := getParam(sig, i).Type()
+		if err := matchType(pkg, arg, typ, at); err != nil {
 			return err
 		}
+		pkg.cb.recordUpdateUntyped(arg, typ)
 	}
 	return nil
 }
@@ -1060,9 +1079,11 @@ func checkFuncResults(pkg *Package, rets []*internal.Elem, results *types.Tuple,
 	}
 	if n == need {
 		for i := 0; i < need; i++ {
-			if err := matchType(pkg, rets[i], results.At(i).Type(), "return argument"); err != nil {
+			typ := results.At(i).Type()
+			if err := matchType(pkg, rets[i], typ, "return argument"); err != nil {
 				panic(err)
 			}
+			pkg.cb.recordUpdateUntyped(rets[i], typ)
 		}
 		return
 	}
@@ -1100,6 +1121,7 @@ func matchElemType(pkg *Package, vals []*internal.Elem, elt types.Type, at inter
 		if err := matchType(pkg, val, elt, at); err != nil {
 			return err
 		}
+		pkg.cb.recordUpdateUntyped(val, elt)
 	}
 	return nil
 }
diff --git a/codebuild.go b/codebuild.go
index ece39978..0583d7aa 100644
--- a/codebuild.go
+++ b/codebuild.go
@@ -828,6 +828,8 @@ func (p *CodeBuilder) MapLit(typ types.Type, arity int, src ...ast.Node) *CodeBu
 					pos, "cannot use %s (type %v) as type %v in map value", src, args[i+1].Type, val)
 			}
 		}
+		p.recordUpdateUntyped(args[i], key)
+		p.recordUpdateUntyped(args[i+1], val)
 	}
 	p.stk.Ret(arity, &internal.Elem{
 		Type: typ, Val: &ast.CompositeLit{Type: typExpr, Elts: elts}, Src: getSrc(src),
@@ -876,6 +878,7 @@ func (p *CodeBuilder) indexElemExpr(args []*internal.Elem, i int) ast.Expr {
 		return args[i+1].Val
 	}
 	p.toIntVal(args[i], "index which must be non-negative integer constant")
+	p.recordUpdateUntyped(args[i], types.Typ[types.Int])
 	return &ast.KeyValueExpr{Key: key, Value: args[i+1].Val}
 }
 
@@ -921,6 +924,7 @@ func (p *CodeBuilder) SliceLitEx(typ types.Type, arity int, keyVal bool, src ...
 				p.panicCodeErrorf(
 					pos, "cannot use %s (type %v) as type %v in slice literal", src, args[i+1].Type, val)
 			}
+			p.recordUpdateUntyped(arg, val)
 			elts[i>>1] = p.indexElemExpr(args, i)
 		}
 	} else {
@@ -956,6 +960,7 @@ func (p *CodeBuilder) SliceLitEx(typ types.Type, arity int, keyVal bool, src ...
 						pos, "cannot use %s (type %v) as type %v in slice literal", src, arg.Type, val)
 				}
 			}
+			p.recordUpdateUntyped(arg, val)
 		}
 	}
 	p.stk.Ret(arity, &internal.Elem{
@@ -1008,6 +1013,7 @@ func (p *CodeBuilder) ArrayLitEx(typ types.Type, arity int, keyVal bool, src ...
 				p.panicCodeErrorf(
 					pos, "cannot use %s (type %v) as type %v in array literal", src, args[i+1].Type, val)
 			}
+			p.recordUpdateUntyped(args[i+1], val)
 			elts[i>>1] = p.indexElemExpr(args, i)
 		}
 	} else {
@@ -1028,6 +1034,7 @@ func (p *CodeBuilder) ArrayLitEx(typ types.Type, arity int, keyVal bool, src ...
 				p.panicCodeErrorf(
 					pos, "cannot use %s (type %v) as type %v in array literal", src, arg.Type, val)
 			}
+			p.recordUpdateUntyped(arg, val)
 		}
 	}
 	p.stk.Ret(arity, &internal.Elem{
@@ -1075,6 +1082,7 @@ func (p *CodeBuilder) StructLit(typ types.Type, arity int, keyVal bool, src ...a
 					pos, "cannot use %s (type %v) as type %v in value of field %s",
 					src, args[i+1].Type, eltTy, eltName)
 			}
+			pkg.cb.recordUpdateUntyped(args[i+1], eltTy)
 			elts[i>>1] = &ast.KeyValueExpr{Key: ident(eltName), Value: args[i+1].Val}
 		}
 	} else if arity != n {
@@ -1097,6 +1105,7 @@ func (p *CodeBuilder) StructLit(typ types.Type, arity int, keyVal bool, src ...a
 					pos, "cannot use %s (type %v) as type %v in value of field %s",
 					src, arg.Type, eltTy, t.Field(i).Name())
 			}
+			pkg.cb.recordUpdateUntyped(arg, eltTy)
 		}
 	}
 	p.stk.Ret(arity, &internal.Elem{
@@ -1145,6 +1154,13 @@ func (p *CodeBuilder) Slice(slice3 bool, src ...ast.Node) *CodeBuilder { // a[i:
 	if slice3 {
 		exprMax = args[3].Val
 	}
+
+	p.recordUpdateUntyped(args[1], tyInt)
+	p.recordUpdateUntyped(args[2], tyInt)
+	if slice3 {
+		p.recordUpdateUntyped(args[3], tyInt)
+	}
+
 	// TODO: check type
 	elem := &internal.Elem{
 		Val: &ast.SliceExpr{
@@ -1185,6 +1201,7 @@ func (p *CodeBuilder) Index(nidx int, twoValue bool, src ...ast.Node) *CodeBuild
 	} else { // elem = a[key]
 		tyRet = typs[1]
 	}
+	p.recordUpdateUntyped(args[1], tyInt)
 	elem := &internal.Elem{
 		Val: &ast.IndexExpr{X: args[0].Val, Index: args[1].Val}, Type: tyRet, Src: srcExpr,
 	}
@@ -1203,6 +1220,7 @@ func (p *CodeBuilder) IndexRef(nidx int, src ...ast.Node) *CodeBuilder {
 	}
 	args := p.stk.GetArgs(2)
 	typ := args[0].Type
+	p.recordUpdateUntyped(args[1], tyInt)
 	elemRef := &internal.Elem{
 		Val: &ast.IndexExpr{X: args[0].Val, Index: args[1].Val},
 		Src: getSrc(src),
@@ -1988,6 +2006,7 @@ func (p *CodeBuilder) doAssignWith(lhs, rhs int, src ast.Node) *CodeBuilder {
 				lhsType = &refType{typ: bfr.typ}
 			}
 			checkAssignType(p.pkg, lhsType, args[lhs+i])
+			p.recordUpdateUntyped(args[lhs+i], lhsType)
 			stmt.Lhs[i] = args[i].Val
 			stmt.Rhs[i] = args[lhs+i].Val
 			if bfAssign {
@@ -2054,6 +2073,7 @@ retry:
 		if !ComparableTo(pkg, args[0], args[1]) {
 			return nil, errors.New("mismatched types")
 		}
+		cb.recordUpdateUntypedBinaryOp(op, args, nil)
 		ret = &internal.Elem{
 			Val: &ast.BinaryExpr{
 				X: checkParenExpr(args[0].Val), Op: op,
@@ -2169,6 +2189,9 @@ func (p *CodeBuilder) Send() *CodeBuilder {
 	val := p.stk.Pop()
 	ch := p.stk.Pop()
 	// TODO: check types
+	if typ, ok := ch.Type.(*types.Chan); ok {
+		p.recordUpdateUntyped(val, typ.Elem())
+	}
 	p.emitStmt(&ast.SendStmt{Chan: ch.Val, Value: val.Val})
 	return p
 }
@@ -2637,3 +2660,64 @@ func (p *CodeBuilder) InternalStack() *InternalStack {
 }
 
 // ----------------------------------------------------------------------------
+
+func (p *CodeBuilder) recordUpdateUntyped(e *internal.Elem, param types.Type) {
+	if p.rec != nil && isBasicUntyped(e.Type) {
+		typ := param
+	retry:
+		switch t := typ.(type) {
+		case *unboundFuncParam:
+			typ = t.tBound
+			goto retry
+		case *refType:
+			typ = t.typ
+			goto retry
+		case *types.Basic:
+			if e.Type == t {
+				return
+			}
+		case *types.Named:
+			if t.Underlying() == TyEmptyInterface {
+				typ = types.Default(e.Type)
+			}
+		case *types.Interface:
+			if t == TyEmptyInterface {
+				typ = types.Default(e.Type)
+			}
+		}
+		p.rec.UpdateUntyped(e, typ)
+	}
+}
+
+func (p *CodeBuilder) recordUpdateUntypedBinaryOp(tok token.Token, args []*internal.Elem, tyRet types.Type) {
+	if p.rec == nil {
+		return
+	}
+	kind := binaryOpKinds[tok]
+	if kind == binaryOpCompare {
+		b0, k0 := isBasicUntypedKind(args[0].Type)
+		b1, k1 := isBasicUntypedKind(args[1].Type)
+		if b0 && !b1 {
+			p.rec.UpdateUntyped(args[0], args[1].Type)
+		} else if !b0 && b1 {
+			p.rec.UpdateUntyped(args[1], args[0].Type)
+		} else if b0 && b1 && k0 != k1 {
+			// UntypedInt
+			// UntypedRune
+			// UntypedFloat
+			// UntypedComplex
+			if k0 < k1 {
+				p.rec.UpdateUntyped(args[0], args[1].Type)
+			} else {
+				p.rec.UpdateUntyped(args[1], args[0].Type)
+			}
+		}
+	} else if tyRet != nil {
+		if isBasicUntyped(args[0].Type) && tyRet != args[0].Type {
+			p.rec.UpdateUntyped(args[0], tyRet)
+		}
+		if kind != binaryOpShift && tyRet != args[1].Type {
+			p.rec.UpdateUntyped(args[1], tyRet)
+		}
+	}
+}
diff --git a/package.go b/package.go
index 861e05b4..b88aba01 100644
--- a/package.go
+++ b/package.go
@@ -73,6 +73,7 @@ func fatal(msg string) {
 type Recorder interface {
 	// Member maps identifiers to the objects they denote.
 	Member(id ast.Node, obj types.Object)
+	UpdateUntyped(e *Element, typ types.Type)
 }
 
 // ----------------------------------------------------------------------------
diff --git a/package_test.go b/package_test.go
index b10031d4..042ba543 100644
--- a/package_test.go
+++ b/package_test.go
@@ -52,6 +52,8 @@ type eventRecorder struct{}
 
 func (p eventRecorder) Member(id ast.Node, obj types.Object) {
 }
+func (p eventRecorder) UpdateUntyped(e *gox.Element, typ types.Type) {
+}
 
 func newMainPackage(
 	implicitCast ...func(pkg *gox.Package, V, T types.Type, pv *gox.Element) bool) *gox.Package {
@@ -3436,4 +3438,41 @@ func main() {
 `)
 }
 
+func TestVarBinary(t *testing.T) {
+	pkg := newMainPackage()
+	pkg.CB().NewVarStart(types.Typ[types.Int], "a").
+		Val(1).
+		EndInit(1).
+		NewVarStart(types.Typ[types.Int], "b").
+		Val(4).Val(pkg.Ref("a")).BinaryOp(token.ADD).
+		EndInit(1).
+		NewVarStart(types.Typ[types.Bool], "c").
+		Val(1).Val(1.0).BinaryOp(token.EQL).EndInit(1).
+		NewVarStart(types.Typ[types.Bool], "d").
+		Val(1.0).Val(1).BinaryOp(token.NEQ).EndInit(1)
+	domTest(t, pkg, `package main
+
+var a int = 1
+var b int = 4 + a
+var c bool = 1 == 1.0
+var d bool = 1.0 != 1
+`)
+}
+
+func TestVarEmptyInterface(t *testing.T) {
+	pkg := newMainPackage()
+	named := pkg.NewType("T").InitType(pkg, gox.TyEmptyInterface)
+	pkg.CB().NewVarStart(named, "a").Val(1).EndInit(1).
+		NewVarStart(gox.TyEmptyInterface, "b").Val(2).EndInit(1)
+	domTest(t, pkg, `package main
+
+type T interface {
+}
+
+var a T = 1
+var b interface {
+} = 2
+`)
+}
+
 // ----------------------------------------------------------------------------
diff --git a/stmt.go b/stmt.go
index 65272102..2b04dbee 100644
--- a/stmt.go
+++ b/stmt.go
@@ -167,11 +167,13 @@ func (p *switchStmt) Case(cb *CodeBuilder, n int, src ...ast.Node) {
 					cb.panicCodeErrorf(
 						pos, "cannot use %s (type %v) as type %v", src, arg.Type, types.Default(p.tag.Type))
 				}
+				cb.recordUpdateUntyped(arg, p.tag.Type)
 			} else { // switch {...}
 				if !types.AssignableTo(arg.Type, types.Typ[types.Bool]) && arg.Type != TyEmptyInterface {
 					src, pos := cb.loadExpr(arg.Src)
 					cb.panicCodeErrorf(pos, "cannot use %s (type %v) as type bool", src, arg.Type)
 				}
+				cb.recordUpdateUntyped(arg, types.Typ[types.Bool])
 			}
 			list[i] = arg.Val
 		}
diff --git a/type_var_and_const.go b/type_var_and_const.go
index 86c01bae..1f803874 100644
--- a/type_var_and_const.go
+++ b/type_var_and_const.go
@@ -328,6 +328,7 @@ func (p *ValueDecl) endInit(cb *CodeBuilder, arity int) *ValueDecl {
 			if err := matchType(pkg, ret, typ, "assignment"); err != nil {
 				panic(err)
 			}
+			cb.recordUpdateUntyped(ret, typ)
 			if values != nil { // ret.Val may be changed
 				values[i] = ret.Val
 			}
@@ -363,6 +364,7 @@ func (p *ValueDecl) endInit(cb *CodeBuilder, arity int) *ValueDecl {
 			if values != nil {
 				values[i] = parg.Val
 			}
+			pkg.cb.recordUpdateUntyped(rets[i], retType)
 			if old := p.scope.Insert(types.NewVar(p.pos, pkg.Types, name, retType)); old != nil {
 				if p.tok != token.DEFINE {
 					oldpos := cb.fset.Position(old.Pos())