diff --git a/lldb/source/Core/Communication.cpp b/lldb/source/Core/Communication.cpp
--- a/lldb/source/Core/Communication.cpp
+++ b/lldb/source/Core/Communication.cpp
@@ -359,7 +359,7 @@
   // Let clients know that this thread is exiting
   comm->BroadcastEvent(eBroadcastBitNoMorePendingInput);
   comm->BroadcastEvent(eBroadcastBitReadThreadDidExit);
-  return nullptr;
+  return lldb::thread_result_t();
 }
 
 void Communication::SetReadThreadBytesReceivedCallback(
diff --git a/lldb/source/Core/Debugger.cpp b/lldb/source/Core/Debugger.cpp
--- a/lldb/source/Core/Debugger.cpp
+++ b/lldb/source/Core/Debugger.cpp
@@ -1616,7 +1616,7 @@
 
 lldb::thread_result_t Debugger::EventHandlerThread(lldb::thread_arg_t arg) {
   ((Debugger *)arg)->DefaultEventHandler();
-  return nullptr;
+  return lldb::thread_result_t();
 }
 
 bool Debugger::StartEventHandlerThread() {