diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index a18650aadb6e93..97b280bb073f8f 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -872,8 +872,13 @@ void mapped_file_region::unmapImpl() {
 
 void mapped_file_region::dontNeedImpl() {
   assert(Mode == mapped_file_region::readonly);
+#if defined(__MVS__) || defined(_AIX)
+  // If we don't have madvise, or it isn't beneficial, treat this as a no-op.
+  return;
+#else
   if (Mapping)
     ::madvise(Mapping, Size, MADV_DONTNEED);
+#endif
 }
 
 int mapped_file_region::alignment() {