diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -123,9 +123,13 @@
 #define LLVM_EXTERNAL_VISIBILITY
 #endif
 #else
-#define LLVM_LIBRARY_VISIBILITY
+#if defined(_WIN32)
+#define LLVM_EXTERNAL_VISIBILITY __declspec(dllexport)
+#esle
 #define LLVM_EXTERNAL_VISIBILITY
 #endif
+#define LLVM_LIBRARY_VISIBILITY
+#endif
 
 #if defined(__GNUC__)
 #define LLVM_PREFETCH(addr, rw, locality) __builtin_prefetch(addr, rw, locality)