Index: tools/debugserver/source/RNBContext.h
===================================================================
--- tools/debugserver/source/RNBContext.h
+++ tools/debugserver/source/RNBContext.h
@@ -86,6 +86,7 @@
     if (arg)
       m_env_vec.push_back(arg);
   }
+  void PushEnvironmentIfNeeded(const char *arg);
   void ClearEnvironment() {
     m_env_vec.erase(m_env_vec.begin(), m_env_vec.end());
   }
Index: tools/debugserver/source/RNBContext.cpp
===================================================================
--- tools/debugserver/source/RNBContext.cpp
+++ tools/debugserver/source/RNBContext.cpp
@@ -42,6 +42,25 @@
     return NULL;
 }
 
+static std::string GetEnvironmentKey(const std::string &env) {
+  std::string key = env.substr(0, env.find('='));
+  if (!key.empty() && key.back() == '=')
+    key.pop_back();
+  return key;
+}
+
+void RNBContext::PushEnvironmentIfNeeded(const char *arg) {
+  if (!arg)
+    return;
+  std::string arg_key = GetEnvironmentKey(arg);
+
+  for (const std::string &entry: m_env_vec) {
+    if (arg_key == GetEnvironmentKey(entry))
+      return;
+  }
+  m_env_vec.push_back(arg);
+}
+
 const char *RNBContext::ArgumentAtIndex(size_t index) {
   if (index < m_arg_vec.size())
     return m_arg_vec[index].c_str();
Index: tools/debugserver/source/debugserver.cpp
===================================================================
--- tools/debugserver/source/debugserver.cpp
+++ tools/debugserver/source/debugserver.cpp
@@ -1020,6 +1020,7 @@
   optind = 1;
 #endif
 
+  bool forward_env = false;
   while ((ch = getopt_long_only(argc, argv, short_options, g_long_options,
                                 &long_option_index)) != -1) {
     DNBLogDebug("option: ch == %c (0x%2.2x) --%s%c%s\n", ch, (uint8_t)ch,
@@ -1251,14 +1252,7 @@
       break;
 
     case 'F':
-      // Pass the current environment down to the process that gets launched
-      {
-        char **host_env = *_NSGetEnviron();
-        char *env_entry;
-        size_t i;
-        for (i = 0; (env_entry = host_env[i]) != NULL; ++i)
-          remote->Context().PushEnvironment(env_entry);
-      }
+      forward_env = true;
       break;
 
     case '2':
@@ -1420,6 +1414,18 @@
   if (start_mode == eRNBRunLoopModeExit)
     return -1;
 
+  if (forward_env || start_mode == eRNBRunLoopModeInferiorLaunching) {
+    // Pass the current environment down to the process that gets launched
+    // This happens automatically in the "launching" mode. For the rest, we
+    // only do that if the user explicitly requested this via --forward-env
+    // argument.
+    char **host_env = *_NSGetEnviron();
+    char *env_entry;
+    size_t i;
+    for (i = 0; (env_entry = host_env[i]) != NULL; ++i)
+      remote->Context().PushEnvironmentIfNeeded(env_entry);
+  }
+
   RNBRunLoopMode mode = start_mode;
   char err_str[1024] = {'\0'};
 
Index: unittests/tools/lldb-server/CMakeLists.txt
===================================================================
--- unittests/tools/lldb-server/CMakeLists.txt
+++ unittests/tools/lldb-server/CMakeLists.txt
@@ -13,9 +13,9 @@
 add_lldb_test_executable(environment_check inferior/environment_check.cpp)
 
 if (CMAKE_SYSTEM_NAME MATCHES "Darwin")
-  add_definitions(-DLLDB_SERVER="$<TARGET_FILE:debugserver>")
+  add_definitions(-DLLDB_SERVER="$<TARGET_FILE:debugserver>" -DLLDB_SERVER_IS_DEBUGSERVER=1)
 else()
-  add_definitions(-DLLDB_SERVER="$<TARGET_FILE:lldb-server>")
+  add_definitions(-DLLDB_SERVER="$<TARGET_FILE:lldb-server>" -DLLDB_SERVER_IS_DEBUGSERVER=0)
 endif()
 
 add_definitions(
Index: unittests/tools/lldb-server/tests/LLGSTest.cpp
===================================================================
--- unittests/tools/lldb-server/tests/LLGSTest.cpp
+++ unittests/tools/lldb-server/tests/LLGSTest.cpp
@@ -16,11 +16,6 @@
 using namespace llvm;
 
 TEST_F(TestBase, LaunchModePreservesEnvironment) {
-  if (TestClient::IsDebugServer()) {
-    GTEST_LOG_(WARNING) << "Test fails with debugserver: llvm.org/pr35671";
-    return;
-  }
-
   putenv(const_cast<char *>("LLDB_TEST_MAGIC_VARIABLE=LLDB_TEST_MAGIC_VALUE"));
 
   auto ClientOr = TestClient::launch(getLogFileName(),
@@ -34,3 +29,20 @@
       HasValue(testing::Property(&StopReply::getKind,
                                  WaitStatus{WaitStatus::Exit, 0})));
 }
+
+TEST_F(TestBase, DS_TEST(DebugserverEnv)) {
+  // Test that --env takes precedence over inherited environment variables.
+  putenv(const_cast<char *>("LLDB_TEST_MAGIC_VARIABLE=foobar"));
+
+  auto ClientOr = TestClient::launchCustom(getLogFileName(),
+      { "--env", "LLDB_TEST_MAGIC_VARIABLE=LLDB_TEST_MAGIC_VALUE" },
+                                     {getInferiorPath("environment_check")});
+  ASSERT_THAT_EXPECTED(ClientOr, Succeeded());
+  auto &Client = **ClientOr;
+
+  ASSERT_THAT_ERROR(Client.ContinueAll(), Succeeded());
+  ASSERT_THAT_EXPECTED(
+      Client.GetLatestStopReplyAs<StopReplyExit>(),
+      HasValue(testing::Property(&StopReply::getKind,
+                                 WaitStatus{WaitStatus::Exit, 0})));
+}
Index: unittests/tools/lldb-server/tests/TestClient.h
===================================================================
--- unittests/tools/lldb-server/tests/TestClient.h
+++ unittests/tools/lldb-server/tests/TestClient.h
@@ -21,12 +21,20 @@
 #include <memory>
 #include <string>
 
+#if LLDB_SERVER_IS_DEBUGSERVER
+#define LLGS_TEST(x) DISABLED_ ## x
+#define DS_TEST(x) x
+#else
+#define LLGS_TEST(x) x
+#define DS_TEST(x) DISABLED_ ## x
+#endif
+
 namespace llgs_tests {
 class TestClient
     : public lldb_private::process_gdb_remote::GDBRemoteCommunicationClient {
 public:
-  static bool IsDebugServer();
-  static bool IsLldbServer();
+  static bool IsDebugServer() { return LLDB_SERVER_IS_DEBUGSERVER; }
+  static bool IsLldbServer() { return !IsDebugServer(); }
 
   /// Launches the server, connects it to the client and returns the client. If
   /// Log is non-empty, the server will write it's log to this file.
@@ -37,6 +45,13 @@
   static llvm::Expected<std::unique_ptr<TestClient>>
   launch(llvm::StringRef Log, llvm::ArrayRef<llvm::StringRef> InferiorArgs);
 
+  /// Allows user to pass additional arguments to the server. Be careful when
+  /// using this for generic tests, as the two stubs have different
+  /// command-line interfaces.
+  static llvm::Expected<std::unique_ptr<TestClient>>
+  launchCustom(llvm::StringRef Log, llvm::ArrayRef<llvm::StringRef> ServerArgs, llvm::ArrayRef<llvm::StringRef> InferiorArgs);
+
+
   ~TestClient() override;
   llvm::Error SetInferior(llvm::ArrayRef<std::string> inferior_args);
   llvm::Error ListThreadsInStopReply();
Index: unittests/tools/lldb-server/tests/TestClient.cpp
===================================================================
--- unittests/tools/lldb-server/tests/TestClient.cpp
+++ unittests/tools/lldb-server/tests/TestClient.cpp
@@ -27,11 +27,6 @@
 using namespace llvm;
 
 namespace llgs_tests {
-bool TestClient::IsDebugServer() {
-  return sys::path::filename(LLDB_SERVER).contains("debugserver");
-}
-
-bool TestClient::IsLldbServer() { return !IsDebugServer(); }
 
 TestClient::TestClient(std::unique_ptr<Connection> Conn) {
   SetConnection(Conn.release());
@@ -56,6 +51,10 @@
 }
 
 Expected<std::unique_ptr<TestClient>> TestClient::launch(StringRef Log, ArrayRef<StringRef> InferiorArgs) {
+  return launchCustom(Log, {}, InferiorArgs);
+}
+
+Expected<std::unique_ptr<TestClient>> TestClient::launchCustom(StringRef Log, ArrayRef<StringRef> ServerArgs, ArrayRef<StringRef> InferiorArgs) {
   const ArchSpec &arch_spec = HostInfo::GetArchitecture();
   Args args;
   args.AppendArgument(LLDB_SERVER);
@@ -80,6 +79,9 @@
   args.AppendArgument(
       ("localhost:" + Twine(listen_socket.GetLocalPortNumber())).str());
 
+  for (StringRef arg : ServerArgs)
+    args.AppendArgument(arg);
+
   if (!InferiorArgs.empty()) {
     args.AppendArgument("--");
     for (StringRef arg : InferiorArgs)