diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1942,12 +1942,7 @@
     ComplexPairTy ComplexVal = EmitComplexExpr(E->getArg(0));
     Value *Real = ComplexVal.first;
     Value *Imag = ComplexVal.second;
-    Value *Zero =
-      Imag->getType()->isFPOrFPVectorTy()
-        ? llvm::ConstantFP::getZeroValueForNegation(Imag->getType())
-        : llvm::Constant::getNullValue(Imag->getType());
-
-    Imag = Builder.CreateFSub(Zero, Imag, "sub");
+    Imag = Builder.CreateFNeg(Imag, "neg");
     return RValue::getComplex(std::make_pair(Real, Imag));
   }
   case Builtin::BI__builtin_creal:
diff --git a/clang/test/CodeGen/complex-builtins-2.c b/clang/test/CodeGen/complex-builtins-2.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/complex-builtins-2.c
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -w -S -o - -emit-llvm              %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -w -S -o - -emit-llvm -fmath-errno %s | FileCheck %s
+
+float _Complex test__builtin_conjf(float _Complex x) {
+// CHECK-LABEL: @test__builtin_conjf(
+// CHECK: fneg float %x.imag
+  return __builtin_conjf(x);
+}
+
+double _Complex test__builtin_conj(double _Complex x) {
+// CHECK-LABEL: @test__builtin_conj(
+// CHECK: fneg double %x.imag
+  return __builtin_conj(x);
+}
+
+long double _Complex test__builtin_conjl(long double _Complex x) {
+// CHECK-LABEL: @test__builtin_conjl(
+// CHECK: fneg x86_fp80 %x.imag
+  return __builtin_conjl(x);
+}