Index: lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h
===================================================================
--- lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h
+++ lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h
@@ -334,7 +334,8 @@
   // and response times.
   bool SendSpeedTestPacket(uint32_t send_size, uint32_t recv_size);
 
-  bool SetCurrentThread(uint64_t tid);
+  bool SetCurrentThread(uint64_t tid,
+                        lldb::pid_t pid = LLDB_INVALID_PROCESS_ID);
 
   bool SetCurrentThreadForRun(uint64_t tid);
 
@@ -567,6 +568,7 @@
       m_supports_jModulesInfo : 1;
 
   lldb::pid_t m_curr_pid;
+  lldb::pid_t m_override_pid; // Used when handling forks
   lldb::tid_t m_curr_tid; // Current gdb remote protocol thread index for all
                           // other operations
   lldb::tid_t m_curr_tid_run; // Current gdb remote protocol thread index for
Index: lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
===================================================================
--- lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -98,7 +98,9 @@
       m_supports_QEnvironmentHexEncoded(true), m_supports_qSymbol(true),
       m_qSymbol_requests_done(false), m_supports_qModuleInfo(true),
       m_supports_jThreadsInfo(true), m_supports_jModulesInfo(true),
-      m_curr_pid(LLDB_INVALID_PROCESS_ID), m_curr_tid(LLDB_INVALID_THREAD_ID),
+      m_curr_pid(LLDB_INVALID_PROCESS_ID),
+      m_override_pid(LLDB_INVALID_PROCESS_ID),
+      m_curr_tid(LLDB_INVALID_THREAD_ID),
       m_curr_tid_run(LLDB_INVALID_THREAD_ID),
       m_num_supported_hardware_watchpoints(0), m_host_arch(), m_process_arch(),
       m_os_build(), m_os_kernel(), m_hostname(), m_gdb_server_name(),
@@ -2598,22 +2600,32 @@
   return false;
 }
 
-bool GDBRemoteCommunicationClient::SetCurrentThread(uint64_t tid) {
-  if (m_curr_tid == tid)
+bool GDBRemoteCommunicationClient::SetCurrentThread(uint64_t tid,
+                                                    lldb::pid_t pid) {
+  if (m_curr_tid == tid && m_override_pid == pid)
     return true;
 
-  char packet[32];
-  int packet_len;
+  lldb_private::StreamString packet;
+  packet.PutCString("Hg");
+  if (m_override_pid != pid) {
+    if (pid == LLDB_INVALID_PROCESS_ID) {
+      assert(m_curr_pid != LLDB_INVALID_PROCESS_ID);
+      pid = m_curr_pid;
+    }
+    packet.PutChar('p');
+    packet.PutHex64(pid);
+    packet.PutChar('.');
+  }
   if (tid == UINT64_MAX)
-    packet_len = ::snprintf(packet, sizeof(packet), "Hg-1");
+    packet.PutCString("-1");
   else
-    packet_len = ::snprintf(packet, sizeof(packet), "Hg%" PRIx64, tid);
-  assert(packet_len + 1 < (int)sizeof(packet));
-  UNUSED_IF_ASSERT_DISABLED(packet_len);
+    packet.PutHex64(tid);
+
   StringExtractorGDBRemote response;
-  if (SendPacketAndWaitForResponse(packet, response, false) ==
+  if (SendPacketAndWaitForResponse(packet.GetString(), response, false) ==
       PacketResult::Success) {
     if (response.IsOKResponse()) {
+      m_override_pid = pid;
       m_curr_tid = tid;
       return true;
     }