diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 1f9b8e387..f8d164644 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -36,6 +36,7 @@ Florian Bruhin
 Florian Preinstorfer
 Florian Schulze
 George Alton
+Gleb Nikonorov
 Gonéri Le Bouder
 Hazal Ozturk
 Henk-Jaap Wagenaar
diff --git a/docs/changelog/1534.bugfix.rst b/docs/changelog/1534.bugfix.rst
new file mode 100644
index 000000000..a997d00e0
--- /dev/null
+++ b/docs/changelog/1534.bugfix.rst
@@ -0,0 +1 @@
+Make the ``passenv`` environment setting case sensitive. - by :user:`gnikonorov`
diff --git a/src/tox/config/__init__.py b/src/tox/config/__init__.py
index aa6946708..ee448c3f0 100644
--- a/src/tox/config/__init__.py
+++ b/src/tox/config/__init__.py
@@ -793,7 +793,7 @@ def passenv(testenv_config, value):
             passenv.add("TMPDIR")
         for spec in value:
             for name in os.environ:
-                if fnmatchcase(name.upper(), spec.upper()):
+                if fnmatchcase(name, spec):
                     passenv.add(name)
         return passenv
 
diff --git a/tests/unit/config/test_config.py b/tests/unit/config/test_config.py
index dcf27ff30..5b1ce1c6c 100644
--- a/tests/unit/config/test_config.py
+++ b/tests/unit/config/test_config.py
@@ -1350,6 +1350,21 @@ def test_passenv_from_global_env(self, newconfig, monkeypatch):
         assert "A1" in env.passenv
         assert "A2" in env.passenv
 
+    def test_passenv_is_case_sensitive(self, newconfig, monkeypatch):
+        monkeypatch.setenv("FOO", "upper case foo")
+        monkeypatch.setenv("fOo", "mixed case foo")
+        monkeypatch.setenv("foo", "lower case foo")
+        config = newconfig(
+            """
+            [testenv]
+            passenv=FOO
+        """,
+        )
+        env = config.envconfigs["python"]
+        assert "FOO" in env.passenv
+        assert "fOo" not in env.passenv
+        assert "foo" not in env.passenv
+
     def test_passenv_glob_from_global_env(self, newconfig, monkeypatch):
         monkeypatch.setenv("A1", "a1")
         monkeypatch.setenv("A2", "a2")
diff --git a/tests/unit/test_venv.py b/tests/unit/test_venv.py
index cc8eb1273..b450678e2 100644
--- a/tests/unit/test_venv.py
+++ b/tests/unit/test_venv.py
@@ -788,7 +788,7 @@ def test_env_variables_added_to_pcall(tmpdir, mocksession, newconfig, monkeypatc
 
         [testenv:python]
         commands=python -V
-        passenv = x123
+        passenv = X123
         setenv =
             ENV_VAR = value
             ESCAPED_VAR = \{value\}