diff --git a/src/cmd/compile/internal/gc/sizeof_test.go b/src/cmd/compile/internal/gc/sizeof_test.go
new file mode 100644
index 00000000000..a0ae7ccdb9d
--- /dev/null
+++ b/src/cmd/compile/internal/gc/sizeof_test.go
@@ -0,0 +1,43 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !nacl
+
+package gc
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+// Assert that the size of important structures do not change unexpectedly.
+
+func TestSizeof(t *testing.T) {
+	const _64bit = unsafe.Sizeof(uintptr(0)) == 8
+
+	var tests = []struct {
+		val    interface{} // type as a value
+		_32bit uintptr     // size on 32bit platforms
+		_64bit uintptr     // size on 64bit platforms
+	}{
+		{Flow{}, 52, 88},
+		{Func{}, 104, 184},
+		{Name{}, 52, 80},
+		{Node{}, 92, 144},
+		{Sym{}, 64, 112},
+		{Type{}, 144, 240},
+	}
+
+	for _, tt := range tests {
+		want := tt._32bit
+		if _64bit {
+			want = tt._64bit
+		}
+		got := reflect.TypeOf(tt.val).Size()
+		if want != got {
+			t.Errorf("unsafe.Sizeof(%T): want %d, got %d", tt.val, want, got)
+		}
+	}
+}
diff --git a/src/cmd/internal/obj/sizeof_test.go b/src/cmd/internal/obj/sizeof_test.go
new file mode 100644
index 00000000000..70e62d0f9fc
--- /dev/null
+++ b/src/cmd/internal/obj/sizeof_test.go
@@ -0,0 +1,40 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !nacl
+
+package obj
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+// Assert that the size of important structures do not change unexpectedly.
+
+func TestSizeof(t *testing.T) {
+	const _64bit = unsafe.Sizeof(uintptr(0)) == 8
+
+	var tests = []struct {
+		val    interface{} // type as a value
+		_32bit uintptr     // size on 32bit platforms
+		_64bit uintptr     // size on 64bit platforms
+	}{
+		{Addr{}, 52, 80},
+		{LSym{}, 92, 152},
+		{Prog{}, 196, 288},
+	}
+
+	for _, tt := range tests {
+		want := tt._32bit
+		if _64bit {
+			want = tt._64bit
+		}
+		got := reflect.TypeOf(tt.val).Size()
+		if want != got {
+			t.Errorf("unsafe.Sizeof(%T): want %d, got %d", tt.val, want, got)
+		}
+	}
+}