@@ -0,0 +1 @@
+Fixed ``ValueError: I/O operation on closed file`` crash during capture teardown when the underlying temporary file has been prematurely closed (e.g. by Python 3.14's incremental garbage collector).
@@ -26,6 +26,7 @@
 from typing import NamedTuple
 from typing import TextIO
 from typing import TYPE_CHECKING
+import warnings
 
 
 if TYPE_CHECKING:
@@ -41,6 +42,7 @@
 from _pytest.nodes import File
 from _pytest.nodes import Item
 from _pytest.reports import CollectReport
+from _pytest.warning_types import PytestWarning
 
 
 _CaptureMethod = Literal["fd", "sys", "no", "tee-sys"]
@@ -566,6 +568,17 @@ class FDCaptureBinary(FDCaptureBase[bytes]):
 
     def snap(self) -> bytes:
         self._assert_state("snap", ("started", "suspended"))
+        if self.tmpfile.closed:
+            warnings.warn(
+                PytestWarning(
+                    "capture tmpfile was closed before snap() -- "
+                    "captured output may be lost "
+                    "(likely caused by Python 3.14.0-3.14.4 incremental GC; "
+                    "upgrade to 3.14.5+)"
+                ),
+                stacklevel=1,
+            )
+            return self.EMPTY_BUFFER
         self.tmpfile.seek(0)
         res = self.tmpfile.buffer.read()
         self.tmpfile.seek(0)
@@ -588,6 +601,17 @@ class FDCapture(FDCaptureBase[str]):
 
     def snap(self) -> str:
         self._assert_state("snap", ("started", "suspended"))
+        if self.tmpfile.closed:
+            warnings.warn(
+                PytestWarning(
+                    "capture tmpfile was closed before snap() -- "
+                    "captured output may be lost "
+                    "(likely caused by Python 3.14.0-3.14.4 incremental GC; "
+                    "upgrade to 3.14.5+)"
+                ),
+                stacklevel=1,
+            )
+            return self.EMPTY_BUFFER
         self.tmpfile.seek(0)
         res = self.tmpfile.read()
         self.tmpfile.seek(0)
 
@@ -1129,6 +1129,40 @@ def test_capfd_sys_stdout_mode(self, capfd) -> None:
         assert "b" not in sys.stdout.mode
 
 
+class TestFDCaptureClosedTmpfile:
+    """Regression tests for #14528: snap() on a prematurely closed tmpfile."""
+
+    @pytest.fixture
+    def pipe_fd(self) -> Generator[int]:
+        """Create a throwaway FD via os.pipe() so we don't touch real stdio."""
+        r, w = os.pipe()
+        os.close(r)
+        yield w
+        try:
+            os.close(w)
+        except OSError:
+            pass
+
+    @pytest.mark.parametrize(
+        "cls, empty",
+        [
+            (capture.FDCapture, ""),
+            (capture.FDCaptureBinary, b""),
+        ],
+        ids=["text", "binary"],
+    )
+    def test_snap_returns_empty_on_closed_tmpfile(
+        self, pipe_fd: int, cls: type, empty: str | bytes
+    ) -> None:
+        cap = cls(pipe_fd)
+        cap.start()
+        cap.tmpfile.close()
+        with pytest.warns(pytest.PytestWarning, match="capture tmpfile was closed"):
+            result = cap.snap()
+        assert result == empty
+        cap.done()
+
+
 @contextlib.contextmanager
 def saved_fd(fd):
     new_fd = os.dup(fd)
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fixed ``ValueError: I/O operation on closed file`` crash during capture teardown when the underlying temporary file has been prematurely closed (e.g. by Python 3.14's incremental garbage collector).