diff --git a/clang/lib/Basic/Targets/OSTargets.h b/clang/lib/Basic/Targets/OSTargets.h
--- a/clang/lib/Basic/Targets/OSTargets.h
+++ b/clang/lib/Basic/Targets/OSTargets.h
@@ -232,15 +232,20 @@
     // setting this to 1 is conforming even if all the basic source
     // character literals have the same encoding as char and wchar_t.
     Builder.defineMacro("__STDC_MB_MIGHT_NEQ_WC__", "1");
+
+    if (this->HasFloat128)
+      Builder.defineMacro("__FLOAT128__");
   }
 
 public:
   FreeBSDTargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : OSTargetInfo<Target>(Triple, Opts) {
     switch (Triple.getArch()) {
-    default:
     case llvm::Triple::x86:
     case llvm::Triple::x86_64:
+      this->HasFloat128 = true;
+      [[fallthrough]];
+    default:
       this->MCountName = ".mcount";
       break;
     case llvm::Triple::mips: