Index: tools/libclang/CIndex.cpp
===================================================================
--- tools/libclang/CIndex.cpp
+++ tools/libclang/CIndex.cpp
@@ -3504,6 +3504,12 @@
         CIdx, source_filename, command_line_args, num_command_line_args,
         llvm::makeArrayRef(unsaved_files, num_unsaved_files), options, out_TU);
   };
+
+  if (getenv("LIBCLANG_NOTHREADS")) {
+    ParseTranslationUnitImpl();
+    return result;
+  }
+
   llvm::CrashRecoveryContext CRC;
 
   if (!RunSafely(CRC, ParseTranslationUnitImpl)) {