diff --git a/include/dxc/Support/WinAdapter.h b/include/dxc/Support/WinAdapter.h
index 311ed522af..ac96f63b0c 100644
--- a/include/dxc/Support/WinAdapter.h
+++ b/include/dxc/Support/WinAdapter.h
@@ -45,10 +45,6 @@
 #define CoTaskMemAlloc malloc
 #define CoTaskMemFree free
 
-#define SysFreeString free
-#define SysAllocStringLen(ptr, size)                                           \
-  (wchar_t *)realloc(ptr, (size + 1) * sizeof(wchar_t))
-
 #define ARRAYSIZE(array) (sizeof(array) / sizeof(array[0]))
 
 #define _countof(a) (sizeof(a) / sizeof(*(a)))
@@ -916,6 +912,12 @@ class CHeapPtr : public CHeapPtrBase<T, Allocator> {
 
 #define CComHeapPtr CHeapPtr
 
+//===--------------------------- BSTR Allocation --------------------------===//
+
+void SysFreeString(BSTR bstrString);
+// Allocate string with length prefix
+BSTR SysAllocStringLen(const OLECHAR *strIn, UINT ui);
+
 //===--------------------- UTF-8 Related Types ----------------------------===//
 
 // Code Page
diff --git a/lib/DxcSupport/WinAdapter.cpp b/lib/DxcSupport/WinAdapter.cpp
index da2a17899c..dcc6303cc6 100644
--- a/lib/DxcSupport/WinAdapter.cpp
+++ b/lib/DxcSupport/WinAdapter.cpp
@@ -68,6 +68,36 @@ void *CAllocator::Reallocate(void *p, size_t nBytes) throw() {
 void *CAllocator::Allocate(size_t nBytes) throw() { return malloc(nBytes); }
 void CAllocator::Free(void *p) throw() { free(p); }
 
+//===--------------------------- BSTR Allocation --------------------------===//
+
+void SysFreeString(BSTR bstrString) {
+  if (bstrString)
+    free((void *)((uintptr_t)bstrString - sizeof(uint32_t)));
+}
+
+// Allocate string with length prefix
+// https://docs.microsoft.com/en-us/previous-versions/windows/desktop/automat/bstr
+BSTR SysAllocStringLen(const OLECHAR *strIn, UINT ui) {
+  uint32_t *blobOut =
+      (uint32_t *)malloc(sizeof(uint32_t) + (ui + 1) * sizeof(OLECHAR));
+
+  if (!blobOut)
+    return nullptr;
+
+  // Size in bytes without trailing NULL character
+  blobOut[0] = ui * sizeof(OLECHAR);
+
+  BSTR strOut = (BSTR)&blobOut[1];
+
+  if (strIn)
+    memcpy(strOut, strIn, blobOut[0]);
+
+  // Write trailing NULL character:
+  strOut[ui] = 0;
+
+  return strOut;
+}
+
 //===---------------------- Char converstion ------------------------------===//
 
 const char *CPToLocale(uint32_t CodePage) {