diff --git a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
--- a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
@@ -361,8 +361,8 @@
 #elif defined(_WIN32)
 
       if (!UnmapViewOfFile(Reservations[Base].LocalAddr))
-        joinErrors(std::move(Err),
-                   errorCodeToError(mapWindowsError(GetLastError())));
+        Err = joinErrors(std::move(Err),
+                         errorCodeToError(mapWindowsError(GetLastError())));
 
 #endif