diff --git a/HISTORY.rst b/HISTORY.rst
index c6a5b99..311012b 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,6 +1,11 @@
 =======
 History
 =======
+
+1.0.2 (2019-05-20)
+------------------
+
+* Stop environment override variables leaking into the process environment
 
 1.0.1 (2019-04-16)
 ------------------
diff --git a/procrunner/__init__.py b/procrunner/__init__.py
index b6560de..e508dea 100644
--- a/procrunner/__init__.py
+++ b/procrunner/__init__.py
@@ -3,7 +3,6 @@
 from __future__ import absolute_import, division, print_function
 
 import codecs
-import copy
 import logging
 import os
 import select
@@ -438,9 +437,8 @@
     if environment is not None:
         env = {key: _path_resolve(environment[key]) for key in environment}
     else:
-        env = os.environ
+        env = {key: value for key, value in os.environ.items()}
     if environment_override:
-        env = copy.copy(env)
         env.update(
             {
                 key: str(_path_resolve(environment_override[key]))
diff --git a/tests/test_procrunner_system.py b/tests/test_procrunner_system.py
index f4fd500..5955463 100644
--- a/tests/test_procrunner_system.py
+++ b/tests/test_procrunner_system.py
@@ -58,11 +58,15 @@
     sentinel_value = b"sentinel"
     tmpdir.join("tempfile").write(sentinel_value)
     tmpdir.join("reader.py").write("print(open('tempfile').read())")
+    assert "LEAK_DETECTOR" not in os.environ
     result = procrunner.run(
         [sys.executable, tmpdir.join("reader.py")],
-        environment_override={"PYTHONHASHSEED": "random"},
+        environment_override={"PYTHONHASHSEED": "random", "LEAK_DETECTOR": "1"},
         working_directory=tmpdir,
     )
     assert result.returncode == 0
     assert not result.stderr
     assert sentinel_value == result.stdout.strip()
+    assert (
+        "LEAK_DETECTOR" not in os.environ
+    ), "overridden environment variable leaked into parent process"