diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index 6ba1b87ea942a90..5e28a8ada595ef1 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -2539,7 +2539,7 @@ Alternatively you can just use ``vars(my_mock)`` (instance members) and
 mock_open
 ~~~~~~~~~
 
-.. function:: mock_open(mock=None, read_data=None)
+.. function:: mock_open(mock=None, read_data='')
 
    A helper function to create a mock to replace the use of :func:`open`. It works
    for :func:`open` called directly or used as a context manager.
diff --git a/Misc/NEWS.d/next/Library/2026-06-13-04-11-00.gh-issue-151426.f2V67e.rst b/Misc/NEWS.d/next/Library/2026-06-13-04-11-00.gh-issue-151426.f2V67e.rst
new file mode 100644
index 000000000000000..428302e5f847f36
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-13-04-11-00.gh-issue-151426.f2V67e.rst
@@ -0,0 +1,4 @@
+Fix impossible stack traces (callers and callees cross called, orphans and
+incorrect lines) in the Tachyon profiler when caching frames, by snapshotting
+the stack chunks before walking the frame chain on a cache miss. Patch by
+Maurycy Pawłowski-Wieroński.
diff --git a/Modules/_remote_debugging/frames.c b/Modules/_remote_debugging/frames.c
index d73cd080dc477f3..e7d2a2764390261 100644
--- a/Modules/_remote_debugging/frames.c
+++ b/Modules/_remote_debugging/frames.c
@@ -580,6 +580,14 @@ collect_frames_with_cache(
         return full_hit < 0 ? -1 : 0;
     }
 
+    assert(ctx->chunks != NULL);
+
+    if (ctx->chunks->count == 0) {
+        if (copy_stack_chunks(unwinder, ctx->thread_state_addr, ctx->chunks) < 0) {
+            PyErr_Clear();
+        }
+    }
+
     Py_ssize_t frames_before = PyList_GET_SIZE(ctx->frame_info);
 
     if (process_frame_chain(unwinder, ctx) < 0) {