Index: clang/lib/Basic/Targets.cpp
===================================================================
--- clang/lib/Basic/Targets.cpp
+++ clang/lib/Basic/Targets.cpp
@@ -517,7 +517,7 @@
     case llvm::Triple::FreeBSD:
       return new FreeBSDTargetInfo<X86_64TargetInfo>(Triple, Opts);
     case llvm::Triple::Fuchsia:
-      return new FuchsiaTargetInfo<X86_64TargetInfo>(Triple, Opts);
+      return new FuchsiaX86_64TargetInfo(Triple, Opts);
     case llvm::Triple::KFreeBSD:
       return new KFreeBSDTargetInfo<X86_64TargetInfo>(Triple, Opts);
     case llvm::Triple::Solaris:
Index: clang/lib/Basic/Targets/X86.h
===================================================================
--- clang/lib/Basic/Targets/X86.h
+++ clang/lib/Basic/Targets/X86.h
@@ -848,6 +848,18 @@
 
   const char *getLongDoubleMangling() const override { return "g"; }
 };
+
+// x86_64 Fuchsia target
+class LLVM_LIBRARY_VISIBILITY FuchsiaX86_64TargetInfo
+    : public FuchsiaTargetInfo<X86_64TargetInfo> {
+public:
+  FuchsiaX86_64TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
+      : FuchsiaTargetInfo<X86_64TargetInfo>(Triple, Opts) {
+    LongDoubleFormat = &llvm::APFloat::IEEEquad();
+  }
+};
+
 } // namespace targets
 } // namespace clang
+
 #endif // LLVM_CLANG_LIB_BASIC_TARGETS_X86_H