diff --git a/src/cmd/compile/internal/types2/alias.go b/src/cmd/compile/internal/types2/alias.go
index 2cc57721f9..06dfba1697 100644
--- a/src/cmd/compile/internal/types2/alias.go
+++ b/src/cmd/compile/internal/types2/alias.go
@@ -21,11 +21,14 @@ type Alias struct {
 // NewAlias creates a new Alias type with the given type name and rhs.
 // rhs must not be nil.
 func NewAlias(obj *TypeName, rhs Type) *Alias {
-	return (*Checker)(nil).newAlias(obj, rhs)
+	alias := (*Checker)(nil).newAlias(obj, rhs)
+	// Ensure that alias.actual is set (#65455).
+	unalias(alias)
+	return alias
 }
 
 func (a *Alias) Obj() *TypeName   { return a.obj }
-func (a *Alias) Underlying() Type { return a.actual.Underlying() }
+func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
 func (a *Alias) String() string   { return TypeString(a, nil) }
 
 // Type accessors
@@ -36,24 +39,26 @@ func (a *Alias) String() string   { return TypeString(a, nil) }
 // Consequently, the result is never an alias type.
 func Unalias(t Type) Type {
 	if a0, _ := t.(*Alias); a0 != nil {
-		if a0.actual != nil {
-			return a0.actual
-		}
-		for a := a0; ; {
-			t = a.fromRHS
-			a, _ = t.(*Alias)
-			if a == nil {
-				break
-			}
-		}
-		if t == nil {
-			panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
-		}
-		a0.actual = t
+		return unalias(a0)
 	}
 	return t
 }
 
+func unalias(a0 *Alias) Type {
+	if a0.actual != nil {
+		return a0.actual
+	}
+	var t Type
+	for a := a0; a != nil; a, _ = t.(*Alias) {
+		t = a.fromRHS
+	}
+	if t == nil {
+		panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
+	}
+	a0.actual = t
+	return t
+}
+
 // asNamed returns t as *Named if that is t's
 // actual type. It returns nil otherwise.
 func asNamed(t Type) *Named {
diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index c70d914453..bacba71955 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -2195,6 +2195,12 @@ func TestIssue61737(t *testing.T) {
 	iface.NumMethods() // unlike go/types, there is no Complete() method, so we complete implicitly
 }
 
+func TestNewAlias_Issue65455(t *testing.T) {
+	obj := NewTypeName(nopos, nil, "A", nil)
+	alias := NewAlias(obj, Typ[Int])
+	alias.Underlying() // must not panic
+}
+
 func TestIssue15305(t *testing.T) {
 	const src = "package p; func f() int16; var _ = f(undef)"
 	f := mustParse(src)
diff --git a/src/go/types/alias.go b/src/go/types/alias.go
index 8333a4d9c9..6043c0a984 100644
--- a/src/go/types/alias.go
+++ b/src/go/types/alias.go
@@ -23,11 +23,14 @@ type Alias struct {
 // NewAlias creates a new Alias type with the given type name and rhs.
 // rhs must not be nil.
 func NewAlias(obj *TypeName, rhs Type) *Alias {
-	return (*Checker)(nil).newAlias(obj, rhs)
+	alias := (*Checker)(nil).newAlias(obj, rhs)
+	// Ensure that alias.actual is set (#65455).
+	unalias(alias)
+	return alias
 }
 
 func (a *Alias) Obj() *TypeName   { return a.obj }
-func (a *Alias) Underlying() Type { return a.actual.Underlying() }
+func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
 func (a *Alias) String() string   { return TypeString(a, nil) }
 
 // Type accessors
@@ -38,24 +41,26 @@ func (a *Alias) String() string   { return TypeString(a, nil) }
 // Consequently, the result is never an alias type.
 func Unalias(t Type) Type {
 	if a0, _ := t.(*Alias); a0 != nil {
-		if a0.actual != nil {
-			return a0.actual
-		}
-		for a := a0; ; {
-			t = a.fromRHS
-			a, _ = t.(*Alias)
-			if a == nil {
-				break
-			}
-		}
-		if t == nil {
-			panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
-		}
-		a0.actual = t
+		return unalias(a0)
 	}
 	return t
 }
 
+func unalias(a0 *Alias) Type {
+	if a0.actual != nil {
+		return a0.actual
+	}
+	var t Type
+	for a := a0; a != nil; a, _ = t.(*Alias) {
+		t = a.fromRHS
+	}
+	if t == nil {
+		panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
+	}
+	a0.actual = t
+	return t
+}
+
 // asNamed returns t as *Named if that is t's
 // actual type. It returns nil otherwise.
 func asNamed(t Type) *Named {
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index 0dc5f35dff..52f0009804 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -2196,6 +2196,12 @@ func TestIssue61737(t *testing.T) {
 	iface.Complete()
 }
 
+func TestNewAlias_Issue65455(t *testing.T) {
+	obj := NewTypeName(nopos, nil, "A", nil)
+	alias := NewAlias(obj, Typ[Int])
+	alias.Underlying() // must not panic
+}
+
 func TestIssue15305(t *testing.T) {
 	const src = "package p; func f() int16; var _ = f(undef)"
 	fset := token.NewFileSet()