diff --git a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
--- a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
+++ b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
@@ -400,7 +400,7 @@
 static constexpr unsigned kPtrInUnrankedMemRefDescriptor = 1;
 
 Type LLVMTypeConverter::convertUnrankedMemRefType(UnrankedMemRefType type) {
-  auto rankTy = LLVM::LLVMType::getInt64Ty(llvmDialect);
+  auto rankTy = getIndexType();
   auto ptrTy = LLVM::LLVMType::getInt8PtrTy(llvmDialect);
   return LLVM::LLVMType::getStructTy(rankTy, ptrTy);
 }
diff --git a/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir b/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir
--- a/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir
+++ b/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir
@@ -1326,7 +1326,7 @@
 // CHECK-NEXT: llvm.insertvalue
 // CHECK-NEXT: llvm.insertvalue
 // CHECK-NEXT: llvm.extractvalue %{{.*}}[0] : !llvm.struct<(i64, ptr<i8>)>
-// CHECK32: llvm.extractvalue %{{.*}}[0] : !llvm.struct<(i64, ptr<i8>)>
+// CHECK32: llvm.extractvalue %{{.*}}[0] : !llvm.struct<(i32, ptr<i8>)>
 
 // CHECK-LABEL: func @rank_of_ranked
 // CHECK32-LABEL: func @rank_of_ranked