Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -201,7 +201,8 @@
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND UBSAN_SUPPORTED_ARCH AND
-    OS_NAME MATCHES "Darwin|Linux|FreeBSD")
+    OS_NAME MATCHES "Darwin|Linux|FreeBSD" OR
+    (OS_NAME MATCHES "Windows" AND CMAKE_SIZEOF_VOID_P EQUAL 4))
   set(COMPILER_RT_HAS_UBSAN TRUE)
 else()
   set(COMPILER_RT_HAS_UBSAN FALSE)
Index: lib/ubsan/ubsan_value.h
===================================================================
--- lib/ubsan/ubsan_value.h
+++ lib/ubsan/ubsan_value.h
@@ -16,7 +16,7 @@
 
 // For now, only support Linux, FreeBSD and Darwin. Other platforms should
 // be easy to add, and probably work as-is.
-#if !defined(__linux__) && !defined(__FreeBSD__) && !defined(__APPLE__)
+#if !defined(__linux__) && !defined(__FreeBSD__) && !defined(__APPLE__) && !defined(_WIN32)
 #error "UBSan not supported for this platform!"
 #endif