Index: unittests/Support/ProgramTest.cpp
===================================================================
--- unittests/Support/ProgramTest.cpp
+++ unittests/Support/ProgramTest.cpp
@@ -7,6 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Support/ConvertUTF.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
@@ -58,16 +59,33 @@
 ProgramTestStringArg2("program-test-string-arg2");
 
 static void CopyEnvironment(std::vector<const char *> &out) {
+#ifdef LLVM_ON_WIN32
+  // On Windows we have to take UTF16 encoded env vars and convert them to UTF8.
+  static std::vector<std::string> storage; // Helper storage for converted vars.
+  storage.clear();
+  _wgetenv(L"TMP"); // Populate _wenviron, initially is null
+  wchar_t **envp = _wenviron;
+  assert(envp);
+  while (*envp != nullptr) {
+    auto pathLen = wcslen(*envp);
+    ArrayRef<char> ref{reinterpret_cast<char const *>(*envp),
+                       pathLen * sizeof(wchar_t)};
+    storage.emplace_back();
+    convertUTF16ToUTF8String(ref, storage.back());
+    out.emplace_back(storage.back().c_str());
+    ++envp;
+  }
+#else
 #ifdef __APPLE__
   char **envp = *_NSGetEnviron();
 #else
-  // environ seems to work for Windows and most other Unices.
   char **envp = environ;
 #endif
   while (*envp != nullptr) {
     out.push_back(*envp);
     ++envp;
   }
+#endif
 }
 
 #ifdef LLVM_ON_WIN32