diff --git a/llvm/lib/System/Unix/MappedFile.cpp b/llvm/lib/System/Unix/MappedFile.cpp
index d853ace..7682c23 100644
--- a/llvm/lib/System/Unix/MappedFile.cpp
+++ b/llvm/lib/System/Unix/MappedFile.cpp
@@ -76,7 +76,10 @@
 void* MappedFile::map() {
   if (!isMapped()) {
     int prot = PROT_NONE;
-    int flags = MAP_FILE;
+    int flags = 0;
+#ifdef MAP_FILE
+    flags |= MAP_FILE;
+#endif
     if (options_ == 0) {
       prot = PROT_READ;
       flags = MAP_PRIVATE;