diff --git a/libcxx/utils/libcxx/test/config.py b/libcxx/utils/libcxx/test/config.py
--- a/libcxx/utils/libcxx/test/config.py
+++ b/libcxx/utils/libcxx/test/config.py
@@ -70,7 +70,7 @@
         self.abi_library_root = None
         self.link_shared = self.get_lit_bool('enable_shared', default=True)
         self.debug_build = self.get_lit_bool('debug_build',   default=False)
-        self.exec_env = dict(os.environ)
+        self.exec_env = dict()
         self.use_target = False
         self.use_system_cxx_lib = False
         self.use_clang_verify = False
@@ -125,9 +125,9 @@
             return 'lib' + name + '.a'
 
     def configure(self):
+        self.configure_target_info()
         self.configure_executor()
         self.configure_use_system_cxx_lib()
-        self.configure_target_info()
         self.configure_cxx()
         self.configure_triple()
         self.configure_deployment()
@@ -200,6 +200,9 @@
             te = LocalExecutor()
             if self.lit_config.useValgrind:
                 te = ValgrindExecutor(self.lit_config.valgrindArgs, te)
+
+        te.target_info = self.target_info
+        
         self.executor = te
 
     def configure_target_info(self):
@@ -1202,9 +1205,4 @@
         self.target_info.configure_env(self.exec_env)
 
     def add_path(self, dest_env, new_path):
-        if 'PATH' not in dest_env:
-            dest_env['PATH'] = new_path
-        else:
-            split_char = ';' if platform.system() == 'Windows' else ':'
-            dest_env['PATH'] = '%s%s%s' % (new_path, split_char,
-                                           dest_env['PATH'])
+        self.target_info.add_path(dest_env, new_path)
diff --git a/libcxx/utils/libcxx/test/executor.py b/libcxx/utils/libcxx/test/executor.py
--- a/libcxx/utils/libcxx/test/executor.py
+++ b/libcxx/utils/libcxx/test/executor.py
@@ -6,14 +6,17 @@
 #
 #===----------------------------------------------------------------------===##
 
-import platform
 import os
 
+from pathlib import PurePosixPath
+
 from libcxx.test import tracing
 from libcxx.util import executeCommand
 
-
 class Executor(object):
+    def __init__(self):
+        self.target_info = None
+
     def run(self, exe_path, cmd, local_cwd, file_deps=None, env=None):
         """Execute a command.
             Be very careful not to change shared state in this function.
@@ -29,6 +32,20 @@
         """
         raise NotImplementedError
 
+    def _merge_environments(self, current_env, updated_env):
+        """Merges two execution environments.
+
+        If both environments contain the PATH variables, they are also merged
+        using the proper separator.
+        """
+        result_env = dict(current_env)
+        for k, v in updated_env.items():
+            if k == 'PATH' and self.target_info:
+                self.target_info.add_path(result_env, v)
+            else:
+                result_env[k] = v
+        return result_env
+
 
 class LocalExecutor(Executor):
     def __init__(self):
@@ -39,6 +56,10 @@
         cmd = cmd or [exe_path]
         if work_dir == '.':
             work_dir = os.getcwd()
+
+        if env:
+            env = self._merge_environments(os.environ, env)
+
         out, err, rc = executeCommand(cmd, cwd=work_dir, env=env)
         return (cmd, out, err, rc)
 
@@ -88,6 +109,7 @@
 
 class RemoteExecutor(Executor):
     def __init__(self):
+        super(RemoteExecutor, self).__init__()
         self.local_run = executeCommand
 
     def remote_temp_dir(self):
@@ -120,7 +142,7 @@
         target_cwd = None
         try:
             target_cwd = self.remote_temp_dir()
-            target_exe_path = os.path.join(target_cwd, 'libcxx_test.exe')
+            target_exe_path = str(PurePosixPath(target_cwd) / 'libcxx_test.exe')
             if cmd:
                 # Replace exe_path with target_exe_path.
                 cmd = [c if c != exe_path else target_exe_path for c in cmd]
@@ -183,13 +205,28 @@
         cmd = [scp, '-p', src, remote + ':' + dst]
         self.local_run(cmd)
 
+    def _env_command(self, env):
+        if not env:
+            return []
+
+        env_cmd = ['env']
+
+        for k, v in env.items():
+            if k == 'PATH':
+                # Pick up the existing paths, so we don't lose any commands
+                if self.target_info and self.target_info.is_windows():
+                    env_cmd.append('PATH="%s;%PATH%"' % v)
+                else:
+                    env_cmd.append('PATH="%s:$PATH"' % v)
+            else:
+                env_cmd.append('"%s"="%s"' % (k, v.replace('\\', '\\\\')))
+
+        return env_cmd
+
     def _execute_command_remote(self, cmd, remote_work_dir='.', env=None):
         remote = self.user_prefix + self.host
         ssh_cmd = [self.ssh_command, '-oBatchMode=yes', remote]
-        if env:
-            env_cmd = ['env'] + ['%s="%s"' % (k, v) for k, v in env.items()]
-        else:
-            env_cmd = []
+        env_cmd = self._env_command(env)
         remote_cmd = ' '.join(env_cmd + cmd)
         if remote_work_dir != '.':
             remote_cmd = 'cd ' + remote_work_dir + ' && ' + remote_cmd
diff --git a/libcxx/utils/libcxx/test/target_info.py b/libcxx/utils/libcxx/test/target_info.py
--- a/libcxx/utils/libcxx/test/target_info.py
+++ b/libcxx/utils/libcxx/test/target_info.py
@@ -37,6 +37,16 @@
     def add_sanitizer_features(self, sanitizer_type, features): pass
     def use_lit_shell_default(self): return False
 
+    def add_path(self, dest_env, new_path):
+        if not new_path:
+            return
+        if 'PATH' not in dest_env:
+            dest_env['PATH'] = new_path
+        else:
+            split_char = ';' if self.is_windows() else ':'
+            dest_env['PATH'] = '%s%s%s' % (new_path, split_char,
+                                           dest_env['PATH'])
+
 
 def test_locale(loc):
     assert loc is not None