src/weak/pointer.go      |  5 ++++-
 src/weak/pointer_test.go | 10 ++++++++++
 test/weak.go             | 24 ++++++++++++++++++++++++

diff --git a/src/weak/pointer.go b/src/weak/pointer.go
index 39c512e76d6fe463a2e341ca925e7e8dd4e5ad3a..e9d7420880a7f92105a33a23446d08224090ef9d 100644
--- a/src/weak/pointer.go
+++ b/src/weak/pointer.go
@@ -56,6 +56,9 @@ // allocation may never become nil if it always exists in the same batch as a
 // referenced object. Typically, this batching only happens for tiny
 // (on the order of 16 bytes or less) and pointer-free objects.
 type Pointer[T any] struct {
+	// Mention T in the type definition to prevent conversions
+	// between Pointer types, like we do for sync/atomic.Pointer.
+	_ [0]*T
 	u unsafe.Pointer
 }
 
@@ -69,7 +72,7 @@ 	if ptr != nil {
 		u = runtime_registerWeakPointer(unsafe.Pointer(ptr))
 	}
 	runtime.KeepAlive(ptr)
-	return Pointer[T]{u}
+	return Pointer[T]{u: u}
 }
 
 // Value returns the original pointer used to create the weak pointer.
diff --git a/src/weak/pointer_test.go b/src/weak/pointer_test.go
index e0ef30377e9e81cc3952c9938b7a17bccec9a1eb..70c743381cacf869bd228b7ca334392bcbe9e3d5 100644
--- a/src/weak/pointer_test.go
+++ b/src/weak/pointer_test.go
@@ -6,10 +6,12 @@ package weak_test
 
 import (
 	"context"
+	"internal/goarch"
 	"runtime"
 	"sync"
 	"testing"
 	"time"
+	"unsafe"
 	"weak"
 )
 
@@ -152,6 +154,14 @@ 	// The weak pointer should still be nil after the finalizer runs.
 	runtime.GC()
 	if wt.Value() != nil {
 		t.Errorf("weak pointer is non-nil even after finalization: %v", wt)
+	}
+}
+
+func TestPointerSize(t *testing.T) {
+	var p weak.Pointer[T]
+	size := unsafe.Sizeof(p)
+	if size != goarch.PtrSize {
+		t.Errorf("weak.Pointer[T] size = %d, want %d", size, goarch.PtrSize)
 	}
 }
 
diff --git a/test/weak.go b/test/weak.go
new file mode 100644
index 0000000000000000000000000000000000000000..ca3ec797fc23662f8192644ea8f3d20be86fd4f2
--- /dev/null
+++ b/test/weak.go
@@ -0,0 +1,24 @@
+// errorcheck
+
+// Copyright 2025 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.
+
+// Test weak pointers.
+
+package p
+
+import (
+	"runtime"
+	"weak"
+)
+
+// Adapted from example in https://github.com/golang/go/issues/67552#issuecomment-2639661220
+func conversion() {
+	p := "hello"
+	a := weak.Make(&p)
+	b := (weak.Pointer[*byte])(a) // ERROR "cannot convert a \(variable of struct type weak\.Pointer\[string\]\) to type weak.Pointer\[\*byte\]"
+	c := b.Value()
+	println(**c)
+	runtime.KeepAlive(p)
+}