Index: wasm/LTO.cpp
===================================================================
--- wasm/LTO.cpp
+++ wasm/LTO.cpp
@@ -45,10 +45,13 @@
   lto::Config C;
   C.Options = InitTargetOptionsFromCodeGenFlags();
 
-  // Always emit a section per function/datum with LTO.
+  // Always emit a section per function/data with LTO.
   C.Options.FunctionSections = true;
   C.Options.DataSections = true;
 
+  // Wasm currently only supports ThreadModel::Single
+  C.Options.ThreadModel = ThreadModel::Single;
+
   C.DisableVerify = Config->DisableVerify;
   C.DiagHandler = diagnosticHandler;
   C.OptLevel = Config->LTOO;