diff --git a/python/tokenspeed/runtime/utils/env.py b/python/tokenspeed/runtime/utils/env.py
index 996ca2d73..213f9901e 100755
--- a/python/tokenspeed/runtime/utils/env.py
+++ b/python/tokenspeed/runtime/utils/env.py
@@ -167,12 +167,14 @@ def override(self, value: Any):
         backup_value = os.environ.get(self.name)
         backup_set_to_none = self._set_to_none
         self.set(value)
-        yield
-        if backup_present:
-            os.environ[self.name] = backup_value
-        else:
-            os.environ.pop(self.name, None)
-        self._set_to_none = backup_set_to_none
+        try:
+            yield
+        finally:
+            if backup_present:
+                os.environ[self.name] = backup_value
+            else:
+                os.environ.pop(self.name, None)
+            self._set_to_none = backup_set_to_none
 
     def clear(self):
         os.environ.pop(self.name, None)
diff --git a/test/runtime/test_env.py b/test/runtime/test_env.py
new file mode 100644
index 000000000..46c8058cb
--- /dev/null
+++ b/test/runtime/test_env.py
@@ -0,0 +1,79 @@
+# Copyright (c) 2026 LightSeek Foundation
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+"""Regression tests for scoped runtime environment overrides."""
+
+import os
+
+import pytest
+
+from tokenspeed.runtime.utils.env import EnvStr
+
+
+class _TestEnvs:
+    TOKENSPEED_TEST_ENV_FIELD_OVERRIDE = EnvStr("default")
+
+
+FIELD = _TestEnvs.TOKENSPEED_TEST_ENV_FIELD_OVERRIDE
+NAME = "TOKENSPEED_TEST_ENV_FIELD_OVERRIDE"
+
+
+def test_override_restores_existing_value_after_exception(monkeypatch):
+    FIELD.clear()
+    monkeypatch.setenv(NAME, "original")
+
+    with pytest.raises(RuntimeError, match="boom"):
+        with FIELD.override("temporary"):
+            assert FIELD.get() == "temporary"
+            raise RuntimeError("boom")
+
+    assert os.environ[NAME] == "original"
+    assert FIELD.get() == "original"
+    assert not FIELD._set_to_none
+
+
+def test_override_restores_missing_value_after_exception(monkeypatch):
+    FIELD.clear()
+    monkeypatch.delenv(NAME, raising=False)
+
+    with pytest.raises(RuntimeError, match="boom"):
+        with FIELD.override("temporary"):
+            assert FIELD.get() == "temporary"
+            raise RuntimeError("boom")
+
+    assert NAME not in os.environ
+    assert FIELD.get() == "default"
+    assert not FIELD._set_to_none
+
+
+def test_override_restores_explicit_none_after_exception():
+    FIELD.clear()
+    FIELD.set(None)
+    try:
+        with pytest.raises(RuntimeError, match="boom"):
+            with FIELD.override("temporary"):
+                assert FIELD.get() == "temporary"
+                raise RuntimeError("boom")
+
+        assert NAME not in os.environ
+        assert FIELD.get() is None
+        assert FIELD._set_to_none
+    finally:
+        FIELD.clear()