Index: lib/CodeGen/TargetInfo.cpp
===================================================================
--- lib/CodeGen/TargetInfo.cpp
+++ lib/CodeGen/TargetInfo.cpp
@@ -3034,7 +3034,7 @@
       return ABIArgInfo::getDirect();
   }
 
-  if (RT || Ty->isMemberPointerType()) {
+  if (RT || Ty->isAnyComplexType() || Ty->isMemberPointerType()) {
     // MS x64 ABI requirement: "Any argument that doesn't fit in 8 bytes, or is
     // not 1, 2, 4, or 8 bytes, must be passed by reference."
     if (Width > 64 || !llvm::isPowerOf2_64(Width))
Index: test/CodeGen/x86_64-arguments-win32.c
===================================================================
--- test/CodeGen/x86_64-arguments-win32.c
+++ test/CodeGen/x86_64-arguments-win32.c
@@ -14,3 +14,9 @@
 
 // CHECK-LABEL: define void @f4(i16 %a)
 void f4(unsigned short a) {}
+
+// CHECK-LABEL: define void @f5(i64 %a.coerce)
+void f5(_Complex float a) {}
+
+// CHECK-LABEL: define void @f6({ double, double }* %a)
+void f6(_Complex double a) {}