diff --git a/lldb/source/API/SystemInitializerFull.cpp b/lldb/source/API/SystemInitializerFull.cpp
--- a/lldb/source/API/SystemInitializerFull.cpp
+++ b/lldb/source/API/SystemInitializerFull.cpp
@@ -17,6 +17,7 @@
 #include "lldb/Target/ProcessTrace.h"
 #include "lldb/Utility/Reproducer.h"
 #include "lldb/Utility/Timer.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/TargetSelect.h"
 
 #pragma clang diagnostic push
@@ -64,6 +65,13 @@
   llvm::InitializeAllAsmPrinters();
   llvm::InitializeAllTargetMCs();
   llvm::InitializeAllDisassemblers();
+  // Initialize the command line parser in LLVM. This usually isn't necessary
+  // as we aren't dealing with command line options here, but otherwise some
+  // other code in Clang/LLVM might be tempted to call this function from a
+  // different thread later on which won't work (as the function isn't
+  // thread-safe).
+  const char *arg0 = "lldb";
+  llvm::cl::ParseCommandLineOptions(1, &arg0);
 
 #define LLDB_PLUGIN(p) LLDB_PLUGIN_INITIALIZE(p);
 #include "Plugins/Plugins.def"