diff --git a/clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp b/clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp
index 2d3bdb522171..c4edbee33dea 100644
--- a/clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp
+++ b/clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp
@@ -364,7 +364,7 @@ void CIRRecordLowering::lowerUnion() {
   }
   // If we have no storage type just pad to the appropriate size and return.
   if (!StorageType)
-    llvm_unreachable("no-storage union NYI");
+    return appendPaddingBytes(LayoutSize);
   // If our storage size was bigger than our required size (can happen in the
   // case of packed bitfields on Itanium) then just use an I8 array.
   if (LayoutSize < getSize(StorageType))
diff --git a/clang/lib/CIR/Dialect/IR/CIRTypes.cpp b/clang/lib/CIR/Dialect/IR/CIRTypes.cpp
index e34232af2d83..a1fa1f7067b0 100644
--- a/clang/lib/CIR/Dialect/IR/CIRTypes.cpp
+++ b/clang/lib/CIR/Dialect/IR/CIRTypes.cpp
@@ -453,8 +453,9 @@ RecordType::computeUnionSize(const mlir::DataLayout &dataLayout) const {
   unsigned recordSize = 0;
   llvm::Align recordAlignment{1};
 
-  auto largestMember = getLargestMember(dataLayout);
-  recordSize = dataLayout.getTypeSize(largestMember);
+  Type largestMember = getLargestMember(dataLayout);
+  if (largestMember)
+    recordSize = dataLayout.getTypeSize(largestMember);
 
   // If the union is padded, add the padding to the size.
   if (getPadded()) {
@@ -517,7 +518,10 @@ RecordType::computeStructAlignment(const mlir::DataLayout &dataLayout) const {
 
 uint64_t
 RecordType::computeUnionAlignment(const mlir::DataLayout &dataLayout) const {
-  auto largestMember = getLargestMember(dataLayout);
+  Type largestMember = getLargestMember(dataLayout);
+  // use 1 byte alignment for empty union
+  if (!largestMember)
+    return 1;
   return dataLayout.getTypeABIAlignment(largestMember);
 }
 
diff --git a/clang/test/CIR/CodeGen/union-empty.cpp b/clang/test/CIR/CodeGen/union-empty.cpp
new file mode 100644
index 000000000000..9fab3134e190
--- /dev/null
+++ b/clang/test/CIR/CodeGen/union-empty.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=LLVM
+
+union EmptyUnion {
+  EmptyUnion() = default;
+};
+
+void f0() {
+  EmptyUnion e;
+};
+
+// CIR: !rec_EmptyUnion = !cir.record<union "EmptyUnion" padded {!u8i}>
+// CIR: cir.func dso_local @_Z2f0v()
+// CIR:   %0 = cir.alloca !rec_EmptyUnion, !cir.ptr<!rec_EmptyUnion>, ["e"] {alignment = 1 : i64}
+// CIR:   cir.return
+
+// LLVM: %union.EmptyUnion = type { i8 }
+// LLVM: define dso_local void @_Z2f0v()
+// LLVM:   %1 = alloca %union.EmptyUnion, i64 1, align 1
+// LLVM:   ret void