diff --git a/changelog/4278.trivial.rst b/changelog/4278.trivial.rst
new file mode 100644
index 00000000000..126cabea859
--- /dev/null
+++ b/changelog/4278.trivial.rst
@@ -0,0 +1 @@
+A CACHEDIR.TAG file gets added to the cache directory.
diff --git a/src/_pytest/cacheprovider.py b/src/_pytest/cacheprovider.py
index 22ce578fc1d..59265ad85f6 100755
--- a/src/_pytest/cacheprovider.py
+++ b/src/_pytest/cacheprovider.py
@@ -33,6 +33,13 @@
 See [the docs](https://docs.pytest.org/en/latest/cache.html) for more information.
 """
 
+CACHEDIR_TAG_CONTENT = b"""\
+Signature: 8a477f597d28d172789f06886806bc55
+# This file is a cache directory tag created by pytest.
+# For information about cache directory tags, see:
+#	http://www.bford.info/cachedir/spec.html
+"""
+
 
 @attr.s
 class Cache(object):
@@ -140,6 +147,10 @@ def _ensure_supporting_files(self):
                 msg = u"# Created by pytest automatically.\n*"
                 gitignore_path.write_text(msg, encoding="UTF-8")
 
+            cachedir_tag_path = self._cachedir.joinpath("CACHEDIR.TAG")
+            if not cachedir_tag_path.is_file():
+                cachedir_tag_path.write_bytes(CACHEDIR_TAG_CONTENT)
+
 
 class LFPlugin(object):
     """ Plugin which implements the --lf (run last-failing) option """
diff --git a/testing/test_cacheprovider.py b/testing/test_cacheprovider.py
index 30fe23aeb5e..29c2d8a1d27 100644
--- a/testing/test_cacheprovider.py
+++ b/testing/test_cacheprovider.py
@@ -925,3 +925,15 @@ def test_does_not_create_boilerplate_in_existing_dirs(testdir):
     assert os.path.isdir("v")  # cache contents
     assert not os.path.exists(".gitignore")
     assert not os.path.exists("README.md")
+
+
+def test_cachedir_tag(testdir):
+    """Ensure we automatically create CACHEDIR.TAG file in the pytest_cache directory (#4278)."""
+    from _pytest.cacheprovider import Cache
+    from _pytest.cacheprovider import CACHEDIR_TAG_CONTENT
+
+    config = testdir.parseconfig()
+    cache = Cache.for_config(config)
+    cache.set("foo", "bar")
+    cachedir_tag_path = cache._cachedir.joinpath("CACHEDIR.TAG")
+    assert cachedir_tag_path.read_bytes() == CACHEDIR_TAG_CONTENT