diff --git a/src/zig_llvm.cpp b/src/zig_llvm.cpp
index 079e73d6e3cc..251faed96eb9 100644
--- a/src/zig_llvm.cpp
+++ b/src/zig_llvm.cpp
@@ -1088,7 +1088,7 @@ void ZigLLVMSetTailCall(LLVMValueRef Call) {
 void ZigLLVMSetCallSret(LLVMValueRef Call, LLVMTypeRef return_type) {
     CallInst *call_inst = unwrap<CallInst>(Call);
     Type *llvm_type = unwrap<Type>(return_type);
-    call_inst->addParamAttr(1, Attribute::getWithStructRetType(call_inst->getContext(), llvm_type));
+    call_inst->addParamAttr(0, Attribute::getWithStructRetType(call_inst->getContext(), llvm_type));
 }
 
 void ZigLLVMFunctionSetPrefixData(LLVMValueRef function, LLVMValueRef data) {