diff --git a/stdlib/@tests/test_cases/check_compression.py b/stdlib/@tests/test_cases/check_compression.py
new file mode 100644
index 000000000000..7fc106f125c7
--- /dev/null
+++ b/stdlib/@tests/test_cases/check_compression.py
@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+import io
+import sys
+from _typeshed import ReadableBuffer
+from bz2 import BZ2Decompressor
+from lzma import LZMADecompressor
+from typing import cast
+from typing_extensions import assert_type
+from zlib import decompressobj
+
+if sys.version_info >= (3, 14):
+    from compression._common._streams import DecompressReader, _Decompressor, _Reader
+    from compression.zstd import ZstdDecompressor
+else:
+    from _compression import DecompressReader, _Decompressor, _Reader
+
+###
+# Tests for DecompressReader/_Decompressor
+###
+
+
+class CustomDecompressor:
+    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes:
+        return b""
+
+    @property
+    def unused_data(self) -> bytes:
+        return b""
+
+    @property
+    def eof(self) -> bool:
+        return False
+
+    @property
+    def needs_input(self) -> bool:
+        return False
+
+
+def accept_decompressor(d: _Decompressor) -> None:
+    d.decompress(b"random bytes", 0)
+    assert_type(d.eof, bool)
+    assert_type(d.unused_data, bytes)
+
+
+fp = cast(_Reader, io.BytesIO(b"hello world"))
+DecompressReader(fp, decompressobj)
+DecompressReader(fp, BZ2Decompressor)
+DecompressReader(fp, LZMADecompressor)
+DecompressReader(fp, CustomDecompressor)
+accept_decompressor(decompressobj())
+accept_decompressor(BZ2Decompressor())
+accept_decompressor(LZMADecompressor())
+accept_decompressor(CustomDecompressor())
+
+if sys.version_info >= (3, 14):
+    DecompressReader(fp, ZstdDecompressor)
+    accept_decompressor(ZstdDecompressor())
diff --git a/stdlib/_compression.pyi b/stdlib/_compression.pyi
index aa67df2ab478..6015bcb13f1c 100644
--- a/stdlib/_compression.pyi
+++ b/stdlib/_compression.pyi
@@ -1,6 +1,6 @@
 # _compression is replaced by compression._common._streams on Python 3.14+ (PEP-784)
 
-from _typeshed import Incomplete, WriteableBuffer
+from _typeshed import ReadableBuffer, WriteableBuffer
 from collections.abc import Callable
 from io import DEFAULT_BUFFER_SIZE, BufferedIOBase, RawIOBase
 from typing import Any, Protocol, type_check_only
@@ -13,13 +13,24 @@ class _Reader(Protocol):
     def seekable(self) -> bool: ...
     def seek(self, n: int, /) -> Any: ...
 
+@type_check_only
+class _Decompressor(Protocol):
+    def decompress(self, data: ReadableBuffer, /, max_length: int = ...) -> bytes: ...
+    @property
+    def unused_data(self) -> bytes: ...
+    @property
+    def eof(self) -> bool: ...
+    # `zlib._Decompress` does not have next property, but `DecompressReader` calls it:
+    # @property
+    # def needs_input(self) -> bool: ...
+
 class BaseStream(BufferedIOBase): ...
 
 class DecompressReader(RawIOBase):
     def __init__(
         self,
         fp: _Reader,
-        decomp_factory: Callable[..., Incomplete],
+        decomp_factory: Callable[..., _Decompressor],
         trailing_error: type[Exception] | tuple[type[Exception], ...] = (),
         **decomp_args: Any,  # These are passed to decomp_factory.
     ) -> None: ...
diff --git a/stdlib/compression/_common/_streams.pyi b/stdlib/compression/_common/_streams.pyi
index b8463973ec67..96aec24d1c2d 100644
--- a/stdlib/compression/_common/_streams.pyi
+++ b/stdlib/compression/_common/_streams.pyi
@@ -1,4 +1,4 @@
-from _typeshed import Incomplete, WriteableBuffer
+from _typeshed import ReadableBuffer, WriteableBuffer
 from collections.abc import Callable
 from io import DEFAULT_BUFFER_SIZE, BufferedIOBase, RawIOBase
 from typing import Any, Protocol, type_check_only
@@ -11,13 +11,24 @@ class _Reader(Protocol):
     def seekable(self) -> bool: ...
     def seek(self, n: int, /) -> Any: ...
 
+@type_check_only
+class _Decompressor(Protocol):
+    def decompress(self, data: ReadableBuffer, /, max_length: int = ...) -> bytes: ...
+    @property
+    def unused_data(self) -> bytes: ...
+    @property
+    def eof(self) -> bool: ...
+    # `zlib._Decompress` does not have next property, but `DecompressReader` calls it:
+    # @property
+    # def needs_input(self) -> bool: ...
+
 class BaseStream(BufferedIOBase): ...
 
 class DecompressReader(RawIOBase):
     def __init__(
         self,
         fp: _Reader,
-        decomp_factory: Callable[..., Incomplete],  # Consider backporting changes to _compression
+        decomp_factory: Callable[..., _Decompressor],  # Consider backporting changes to _compression
         trailing_error: type[Exception] | tuple[type[Exception], ...] = (),
         **decomp_args: Any,  # These are passed to decomp_factory.
     ) -> None: ...