diff --git a/go/types/decl.go b/go/types/decl.go
index 5d170862..c5d89905 100644
--- a/go/types/decl.go
+++ b/go/types/decl.go
@@ -151,6 +151,26 @@ func (check *checker) varDecl(obj *Var, lhs []*Var, typ, init ast.Expr) {
 	check.initVars(lhs, []ast.Expr{init}, token.NoPos)
 }
 
+// underlying returns the underlying type of typ; possibly by following
+// forward chains of named types. Such chains only exist while names types
+// are incomplete.
+func underlying(typ Type) Type {
+	for {
+		n, _ := typ.(*Named)
+		if n == nil {
+			break
+		}
+		typ = n.underlying
+	}
+	return typ
+}
+
+func (n *Named) setUnderlying(typ Type) {
+	if n != nil {
+		n.underlying = typ
+	}
+}
+
 func (check *checker) typeDecl(obj *TypeName, typ ast.Expr, def *Named, cycleOk bool) {
 	assert(obj.Type() == nil)
 
@@ -158,17 +178,14 @@ func (check *checker) typeDecl(obj *TypeName, typ ast.Expr, def *Named, cycleOk
 	assert(check.iota == nil)
 
 	named := &Named{obj: obj}
+	def.setUnderlying(named)
 	obj.typ = named // make sure recursive type declarations terminate
 
-	// If this type (named) defines the type of another (def) type declaration,
-	// set def's underlying type to this type so that we can resolve the true
-	// underlying of def later.
-	if def != nil {
-		def.underlying = named
-	}
+	// determine underlying type of named
+	check.typ(typ, named, cycleOk)
 
-	// Typecheck typ - it may be a named type that is not yet complete.
-	// For instance, consider:
+	// The underlying type of named may be itself a named type that is
+	// incomplete:
 	//
 	//	type (
 	//		A B
@@ -176,21 +193,11 @@ func (check *checker) typeDecl(obj *TypeName, typ ast.Expr, def *Named, cycleOk
 	//		C A
 	//	)
 	//
-	// When we declare object C, typ is the identifier A which is incomplete.
-	u := check.typ(typ, named, cycleOk)
-
-	// Determine the unnamed underlying type.
-	// In the above example, the underlying type of A was (temporarily) set
-	// to B whose underlying type was set to *C. Such "forward chains" always
-	// end in an unnamed type (cycles are terminated with an invalid type).
-	for {
-		n, _ := u.(*Named)
-		if n == nil {
-			break
-		}
-		u = n.underlying
-	}
-	named.underlying = u
+	// The type of C is the (named) type of A which is incomplete,
+	// and which has as its underlying type the named type B.
+	// Determine the (final, unnamed) underlying type by resolving
+	// any forward chain (they always end in an unnamed type).
+	named.underlying = underlying(named.underlying)
 
 	// the underlying type has been determined
 	named.complete = true
@@ -257,14 +264,14 @@ func (check *checker) funcDecl(obj *Func, info *declInfo) {
 	// func declarations cannot use iota
 	assert(check.iota == nil)
 
-	obj.typ = Typ[Invalid] // guard against cycles
+	sig := new(Signature)
+	obj.typ = sig // guard against cycles
 	fdecl := info.fdecl
-	sig := check.funcType(fdecl.Recv, fdecl.Type, nil)
+	check.funcType(sig, fdecl.Recv, fdecl.Type)
 	if sig.recv == nil && obj.name == "init" && (sig.params.Len() > 0 || sig.results.Len() > 0) {
 		check.errorf(fdecl.Pos(), "func init must have no arguments and no return values")
 		// ok to continue
 	}
-	obj.typ = sig
 
 	// function body must be type-checked after global declarations
 	// (functions implemented elsewhere have no body)
diff --git a/go/types/typexpr.go b/go/types/typexpr.go
index 0ca17a88..c8cbd4ed 100644
--- a/go/types/typexpr.go
+++ b/go/types/typexpr.go
@@ -36,7 +36,7 @@ func (check *checker) ident(x *operand, e *ast.Ident, def *Named, cycleOk bool)
 
 	typ := obj.Type()
 	if typ == nil {
-		// object not yet declared
+		// object type not yet determined
 		if check.objMap == nil {
 			check.dump("%s: %s should have been declared (we are inside a function)", e.Pos(), e)
 			unreachable()
@@ -82,9 +82,6 @@ func (check *checker) ident(x *operand, e *ast.Ident, def *Named, cycleOk bool)
 			// maintain x.mode == typexpr despite error
 			typ = Typ[Invalid]
 		}
-		if def != nil {
-			def.underlying = typ
-		}
 
 	case *Var:
 		obj.used = true
@@ -141,12 +138,7 @@ func (check *checker) typ(e ast.Expr, def *Named, cycleOk bool) (T Type) {
 }
 
 // funcType type-checks a function or method type and returns its signature.
-func (check *checker) funcType(recv *ast.FieldList, ftyp *ast.FuncType, def *Named) *Signature {
-	sig := new(Signature)
-	if def != nil {
-		def.underlying = sig
-	}
-
+func (check *checker) funcType(sig *Signature, recv *ast.FieldList, ftyp *ast.FuncType) *Signature {
 	scope := NewScope(check.topScope)
 	check.recordScope(ftyp, scope)
 
@@ -202,7 +194,7 @@ func (check *checker) funcType(recv *ast.FieldList, ftyp *ast.FuncType, def *Nam
 	return sig
 }
 
-// typInternal contains the core of type checking of types.
+// typInternal drives type checking of types.
 // Must only be called by typ.
 //
 func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
@@ -216,7 +208,9 @@ func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
 
 		switch x.mode {
 		case typexpr:
-			return x.typ
+			typ := x.typ
+			def.setUnderlying(typ)
+			return typ
 		case invalid:
 			// ignore - error reported before
 		case novalue:
@@ -231,7 +225,9 @@ func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
 
 		switch x.mode {
 		case typexpr:
-			return x.typ
+			typ := x.typ
+			def.setUnderlying(typ)
+			return typ
 		case invalid:
 			// ignore - error reported before
 		case novalue:
@@ -246,53 +242,45 @@ func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
 	case *ast.ArrayType:
 		if e.Len != nil {
 			typ := new(Array)
-			if def != nil {
-				def.underlying = typ
-			}
-
+			def.setUnderlying(typ)
 			typ.len = check.arrayLength(e.Len)
 			typ.elem = check.typ(e.Elt, nil, cycleOk)
 			return typ
 
 		} else {
 			typ := new(Slice)
-			if def != nil {
-				def.underlying = typ
-			}
-
+			def.setUnderlying(typ)
 			typ.elem = check.typ(e.Elt, nil, true)
 			return typ
 		}
 
 	case *ast.StructType:
 		typ := new(Struct)
-		if def != nil {
-			def.underlying = typ
-		}
-
-		typ.fields, typ.tags = check.collectFields(e.Fields, cycleOk)
+		def.setUnderlying(typ)
+		check.structType(typ, e, cycleOk)
 		return typ
 
 	case *ast.StarExpr:
 		typ := new(Pointer)
-		if def != nil {
-			def.underlying = typ
-		}
-
+		def.setUnderlying(typ)
 		typ.base = check.typ(e.X, nil, true)
 		return typ
 
 	case *ast.FuncType:
-		return check.funcType(nil, e, def)
+		typ := new(Signature)
+		def.setUnderlying(typ)
+		check.funcType(typ, nil, e)
+		return typ
 
 	case *ast.InterfaceType:
-		return check.interfaceType(e, def, cycleOk)
+		typ := new(Interface)
+		def.setUnderlying(typ)
+		check.interfaceType(typ, e, def, cycleOk)
+		return typ
 
 	case *ast.MapType:
 		typ := new(Map)
-		if def != nil {
-			def.underlying = typ
-		}
+		def.setUnderlying(typ)
 
 		typ.key = check.typ(e.Key, nil, true)
 		typ.elem = check.typ(e.Value, nil, true)
@@ -313,9 +301,7 @@ func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
 
 	case *ast.ChanType:
 		typ := new(Chan)
-		if def != nil {
-			def.underlying = typ
-		}
+		def.setUnderlying(typ)
 
 		dir := SendRecv
 		switch e.Dir {
@@ -329,6 +315,7 @@ func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
 			check.invalidAST(e.Pos(), "unknown channel direction %d", e.Dir)
 			// ok to continue
 		}
+
 		typ.dir = dir
 		typ.elem = check.typ(e.Value, nil, true)
 		return typ
@@ -337,7 +324,9 @@ func (check *checker) typInternal(e ast.Expr, def *Named, cycleOk bool) Type {
 		check.errorf(e.Pos(), "%s is not a type", e)
 	}
 
-	return Typ[Invalid]
+	typ := Typ[Invalid]
+	def.setUnderlying(typ)
+	return typ
 }
 
 // typeOrNil type-checks the type expression (or nil value) e
@@ -438,15 +427,10 @@ func (check *checker) declareInSet(oset *objset, pos token.Pos, obj Object) bool
 	return true
 }
 
-func (check *checker) interfaceType(ityp *ast.InterfaceType, def *Named, cycleOk bool) *Interface {
-	iface := new(Interface)
-	if def != nil {
-		def.underlying = iface
-	}
-
+func (check *checker) interfaceType(iface *Interface, ityp *ast.InterfaceType, def *Named, cycleOk bool) {
 	// empty interface: common case
 	if ityp.Methods == nil {
-		return iface
+		return
 	}
 
 	// The parser ensures that field tags are nil and we don't
@@ -501,31 +485,21 @@ func (check *checker) interfaceType(ityp *ast.InterfaceType, def *Named, cycleOk
 	for _, e := range embedded {
 		pos := e.Pos()
 		typ := check.typ(e, nil, cycleOk)
-		if typ == Typ[Invalid] {
-			continue
-		}
 		named, _ := typ.(*Named)
 		if named == nil {
-			check.invalidAST(pos, "%s is not named type", typ)
+			if typ != Typ[Invalid] {
+				check.invalidAST(pos, "%s is not named type", typ)
+			}
 			continue
 		}
 		// determine underlying (possibly incomplete) type
 		// by following its forward chain
-		// TODO(gri) should this be part of Underlying()?
-		u := named.underlying
-		for {
-			n, _ := u.(*Named)
-			if n == nil {
-				break
-			}
-			u = n.underlying
-		}
-		if u == Typ[Invalid] {
-			continue
-		}
+		u := underlying(named)
 		embed, _ := u.(*Interface)
 		if embed == nil {
-			check.errorf(pos, "%s is not an interface", named)
+			if u != Typ[Invalid] {
+				check.errorf(pos, "%s is not an interface", named)
+			}
 			continue
 		}
 		iface.embeddeds = append(iface.embeddeds, named)
@@ -553,12 +527,11 @@ func (check *checker) interfaceType(ityp *ast.InterfaceType, def *Named, cycleOk
 	for i, m := range iface.methods {
 		expr := signatures[i]
 		typ := check.typ(expr, nil, true)
-		if typ == Typ[Invalid] {
-			continue // keep method with empty method signature
-		}
 		sig, _ := typ.(*Signature)
 		if sig == nil {
-			check.invalidAST(expr.Pos(), "%s is not a method signature", typ)
+			if typ != Typ[Invalid] {
+				check.invalidAST(expr.Pos(), "%s is not a method signature", typ)
+			}
 			continue // keep method with empty method signature
 		}
 		sig.recv = NewVar(m.pos, check.pkg, "", recv)
@@ -576,8 +549,6 @@ func (check *checker) interfaceType(ityp *ast.InterfaceType, def *Named, cycleOk
 	sort.Sort(byUniqueTypeName(iface.embeddeds))
 
 	sort.Sort(byUniqueMethodName(iface.allMethods))
-
-	return iface
 }
 
 // byUniqueTypeName named type lists can be sorted by their unique type names.
@@ -606,15 +577,22 @@ func (check *checker) tag(t *ast.BasicLit) string {
 	return ""
 }
 
-func (check *checker) collectFields(list *ast.FieldList, cycleOk bool) (fields []*Var, tags []string) {
+func (check *checker) structType(styp *Struct, e *ast.StructType, cycleOk bool) {
+	list := e.Fields
 	if list == nil {
 		return
 	}
 
+	// struct fields and tags
+	var fields []*Var
+	var tags []string
+
+	// for double-declaration checks
 	var fset objset
 
-	var typ Type   // current field typ
-	var tag string // current field tag
+	// current field typ and tag
+	var typ Type
+	var tag string
 	add := func(field *ast.Field, ident *ast.Ident, name string, anonymous bool, pos token.Pos) {
 		if tag != "" && tags == nil {
 			tags = make([]string, len(fields))
@@ -662,7 +640,7 @@ func (check *checker) collectFields(list *ast.FieldList, cycleOk bool) (fields [
 				// spec: "An embedded type must be specified as a type name
 				// T or as a pointer to a non-interface type name *T, and T
 				// itself may not be a pointer type."
-				switch u := t.Underlying().(type) {
+				switch u := t.underlying.(type) {
 				case *Basic:
 					// unsafe.Pointer is treated like a regular pointer
 					if u.kind == UnsafePointer {
@@ -686,5 +664,6 @@ func (check *checker) collectFields(list *ast.FieldList, cycleOk bool) (fields [
 		}
 	}
 
-	return
+	styp.fields = fields
+	styp.tags = tags
 }