diff --git a/src/pymod/unit_tests/pymod_tests.cc b/src/pymod/unit_tests/pymod_tests.cc
index d523dd344..7ec39f7af 100644
--- a/src/pymod/unit_tests/pymod_tests.cc
+++ b/src/pymod/unit_tests/pymod_tests.cc
@@ -32,19 +32,12 @@
 
 #include "tlUnitTest.h"
 #include "tlStream.h"
+#include "tlEnv.h"
 
 int run_pymodtest (tl::TestBase *_this, const std::string &fn)
 {
-  static std::string pypath;
-  if (pypath.empty ()) {
-    pypath = "PYTHONPATH=";
-    pypath += STRINGIFY (PYTHONPATH);
-  }
-#if defined(_WIN32)
-  _putenv (const_cast<char *> (pypath.c_str ()));
-#else
-  putenv (const_cast<char *> (pypath.c_str ()));
-#endif
+  std::string pypath = STRINGIFY (PYTHONPATH);
+  tl::set_env ("PYTHONPATH", pypath);
   tl::info << pypath;
 
   std::string fp (tl::testdata ());
diff --git a/src/tl/tl/tlEnv.cc b/src/tl/tl/tlEnv.cc
index ffd779ddd..47107818c 100644
--- a/src/tl/tl/tlEnv.cc
+++ b/src/tl/tl/tlEnv.cc
@@ -23,6 +23,7 @@
 
 #include "tlEnv.h"
 #include "tlString.h"
+#include "tlThreads.h"
 
 #include <string>
 
@@ -38,8 +39,13 @@
 namespace tl
 {
 
+static tl::Mutex s_env_lock;
+static std::map<std::string, std::string> s_env_map;
+
 std::string get_env (const std::string &name, const std::string &def_value)
 {
+  tl::MutexLocker env_locker (&s_env_lock);
+
 #ifdef _WIN32
   std::wstring wname = tl::to_wstring (name);
   wchar_t *env = _wgetenv (wname.c_str ());
@@ -58,6 +64,38 @@ std::string get_env (const std::string &name, const std::string &def_value)
 #endif
 }
 
+void set_env (const std::string &name, const std::string &value)
+{
+  tl::MutexLocker env_locker (&s_env_lock);
+
+  s_env_map [name] = name + "=" + value;
+  const std::string &s = s_env_map [name];
+
+#if defined(_WIN32)
+  _putenv (const_cast<char *> (s.c_str ()));
+#else
+  putenv (const_cast<char *> (s.c_str ()));
+#endif
+}
+
+void unset_env (const std::string &name)
+{
+  tl::MutexLocker env_locker (&s_env_lock);
+
+#if defined(_WIN32)
+  s_env_map [name] = name + "=";
+#else
+  s_env_map [name] = name;
+#endif
+  const std::string &s = s_env_map [name];
+
+#if defined(_WIN32)
+  _putenv (const_cast<char *> (s.c_str ()));
+#else
+  putenv (const_cast<char *> (s.c_str ()));
+#endif
+}
+
 bool has_env (const std::string &name)
 {
 #ifdef _WIN32
diff --git a/src/tl/tl/tlEnv.h b/src/tl/tl/tlEnv.h
index 454b68bd8..ca17fdd30 100644
--- a/src/tl/tl/tlEnv.h
+++ b/src/tl/tl/tlEnv.h
@@ -38,6 +38,16 @@ namespace tl
  */
 std::string TL_PUBLIC get_env (const std::string &name, const std::string &def_value = std::string ());
 
+/**
+ *  @brief Sets the value for the given environment variable
+ */
+void TL_PUBLIC set_env (const std::string &name, const std::string &value);
+
+/**
+ *  @brief Removes the given environment variable
+ */
+void TL_PUBLIC unset_env (const std::string &name);
+
 /**
  *  @brief Gets the value if the given environment variable is set
  */
diff --git a/src/tl/unit_tests/tlEnvTests.cc b/src/tl/unit_tests/tlEnvTests.cc
new file mode 100644
index 000000000..46a0f0364
--- /dev/null
+++ b/src/tl/unit_tests/tlEnvTests.cc
@@ -0,0 +1,45 @@
+
+/*
+
+  KLayout Layout Viewer
+  Copyright (C) 2006-2023 Matthias Koefferlein
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+*/
+
+#include "tlEnv.h"
+#include "tlUnitTest.h"
+
+const char *dne_name = "__DOES_NOT_EXIST__";
+
+TEST(1)
+{
+  EXPECT_EQ (tl::has_env (dne_name), false);
+
+  tl::set_env (dne_name, "123");
+  EXPECT_EQ (tl::has_env (dne_name), true);
+
+  EXPECT_EQ (tl::get_env (dne_name), "123");
+
+  tl::set_env (dne_name, "42");
+  EXPECT_EQ (tl::has_env (dne_name), true);
+
+  EXPECT_EQ (tl::get_env (dne_name), "42");
+
+  tl::unset_env (dne_name);
+  EXPECT_EQ (tl::get_env (dne_name, "bla"), "bla");
+  EXPECT_EQ (tl::has_env (dne_name), false);
+}
diff --git a/src/tl/unit_tests/unit_tests.pro b/src/tl/unit_tests/unit_tests.pro
index 2e0bab909..0e4bcc449 100644
--- a/src/tl/unit_tests/unit_tests.pro
+++ b/src/tl/unit_tests/unit_tests.pro
@@ -16,6 +16,7 @@ SOURCES = \
   tlDataMappingTests.cc \
   tlDeferredExecutionTests.cc \
   tlDeflateTests.cc \
+  tlEnvTests.cc \
   tlEventsTests.cc \
   tlExpressionTests.cc \
   tlFileSystemWatcherTests.cc \