@@ -424,6 +424,8 @@ pub struct PyCData {
     pub buffer: PyRwLock<Cow<'static, [u8]>>,
     /// pointer to base object or None (b_base)
     pub base: PyRwLock<Option<PyObjectRef>>,
+    /// Original from_buffer view, independent of the Python-mutable _objects dict.
+    buffer_source: Option<PyObjectRef>,
     /// byte offset within base's buffer (for field access)
     pub base_offset: AtomicCell<usize>,
     /// index into base's b_objects list (b_index)
@@ -445,6 +447,7 @@ impl PyCData {
         Self {
             buffer: PyRwLock::new(Cow::Owned(vec![0u8; stg_info.size])),
             base: PyRwLock::new(None),
+            buffer_source: None,
             base_offset: AtomicCell::new(0),
             index: AtomicCell::new(0),
             objects: PyRwLock::new(None),
@@ -458,6 +461,7 @@ impl PyCData {
         Self {
             buffer: PyRwLock::new(Cow::Owned(data)),
             base: PyRwLock::new(None),
+            buffer_source: None,
             base_offset: AtomicCell::new(0),
             index: AtomicCell::new(0),
             objects: PyRwLock::new(objects),
@@ -475,6 +479,7 @@ impl PyCData {
         Self {
             buffer: PyRwLock::new(Cow::Owned(data)),
             base: PyRwLock::new(None),
+            buffer_source: None,
             base_offset: AtomicCell::new(0),
             index: AtomicCell::new(0),
             objects: PyRwLock::new(objects),
@@ -496,6 +501,7 @@ impl PyCData {
         Self {
             buffer: PyRwLock::new(Cow::Borrowed(slice)),
             base: PyRwLock::new(None),
+            buffer_source: None,
             base_offset: AtomicCell::new(0),
             index: AtomicCell::new(0),
             objects: PyRwLock::new(None),
@@ -525,6 +531,7 @@ impl PyCData {
         Self {
             buffer: PyRwLock::new(Cow::Borrowed(slice)),
             base: PyRwLock::new(Some(base_obj)),
+            buffer_source: None,
             base_offset: AtomicCell::new(0),
             index: AtomicCell::new(idx),
             objects: PyRwLock::new(None),
@@ -554,12 +561,13 @@ impl PyCData {
         // Python stores the reference in a dict with key "-1" (unique_key pattern)
         let objects_dict = vm.ctx.new_dict();
         objects_dict
-            .set_item("-1", source, vm)
+            .set_item("-1", source.clone(), vm)
             .expect("Failed to store buffer reference");
 
         Self {
             buffer: PyRwLock::new(Cow::Borrowed(slice)),
             base: PyRwLock::new(None),
+            buffer_source: Some(source),
             base_offset: AtomicCell::new(0),
             index: AtomicCell::new(0),
             objects: PyRwLock::new(Some(objects_dict.into())),
@@ -568,6 +576,13 @@ impl PyCData {
         }
     }
 
+    /// Storage owner used to detect aliased buffers without consulting _objects.
+    pub(crate) fn buffer_base(&self) -> Option<PyObjectRef> {
+        self.buffer_source
+            .clone()
+            .or_else(|| self.base.read().clone())
+    }
+
     /// Common implementation for from_buffer class method.
     /// Validates buffer, creates memoryview, and returns PyCData sharing memory with source.
     ///
 
@@ -96,7 +96,7 @@ pub(crate) fn ctypes_buffer_base(_obj: &crate::PyObject) -> Option<crate::PyObje
         not(any(target_env = "musl", target_env = "sgx"))
     ))]
     if let Some(cdata) = _obj.downcast_ref::<_ctypes::PyCData>() {
-        return cdata.base.read().clone();
+        return cdata.buffer_base();
     }
     None
 }
 
@@ -500,4 +500,10 @@ class OverlappingFields(ctypes.Union):
 memoryview(overlap.a).cast("B")[::2] = memoryview(overlap.b).cast("B")[:4]
 assert list(overlap.a) == [0, 1, 1, 3, 2, 5, 3, 7]
 
+backing = bytearray(range(8))
+view = (ctypes.c_ubyte * 7).from_buffer(backing, 1)
+view._objects.clear()  # Alias detection must not depend on mutable retention metadata.
+memoryview(view).cast("B")[::2] = memoryview(backing)[:4]
+assert list(backing) == [0, 0, 2, 1, 4, 2, 6, 3]
+
 print("done")
Original file line number	Diff line number	Diff line change
`@@ -96,7 +96,7 @@ pub(crate) fn ctypes_buffer_base(_obj: &crate::PyObject) -> Option<crate::PyObje`
`96`	`96`	`not(any(target_env = "musl", target_env = "sgx"))`
`97`	`97`	`))]`
`98`	`98`	`if let Some(cdata) = _obj.downcast_ref::<_ctypes::PyCData>() {`
`99`		`- return cdata.base.read().clone();`
	`99`	`+ return cdata.buffer_base();`
`100`	`100`	`}`
`101`	`101`	`None`
`102`	`102`	`}`