diff --git a/lib/IRGen/IRGen.cpp b/lib/IRGen/IRGen.cpp
index 815c972e0455b..81a507d587651 100644
--- a/lib/IRGen/IRGen.cpp
+++ b/lib/IRGen/IRGen.cpp
@@ -156,6 +156,14 @@ swift::getIRTargetOptions(IRGenOptions &Opts, ASTContext &Ctx) {
 
   auto *Clang = static_cast<ClangImporter *>(Ctx.getClangModuleLoader());
   clang::TargetOptions &ClangOpts = Clang->getTargetInfo().getTargetOpts();
+
+  // WebAssembly doesn't support atomics or DWARF5 yet.
+  // (LLVM debugger tuning generates a DWARF5 accel table even when DWARF5 is disabled)
+  if (Clang->getTargetInfo().getTriple().isOSBinFormatWasm()) {
+    TargetOpts.DebuggerTuning = llvm::DebuggerKind::Default;
+    TargetOpts.ThreadModel = llvm::ThreadModel::Single;
+  }
+
   return std::make_tuple(TargetOpts, ClangOpts.CPU, ClangOpts.Features, ClangOpts.Triple);
 }