diff --git a/compiler-rt/lib/msan/msan_allocator.cpp b/compiler-rt/lib/msan/msan_allocator.cpp
--- a/compiler-rt/lib/msan/msan_allocator.cpp
+++ b/compiler-rt/lib/msan/msan_allocator.cpp
@@ -192,7 +192,10 @@
       reinterpret_cast<Metadata *>(allocator.GetMetaData(allocated));
   meta->requested_size = size;
   if (zeroise) {
-    __msan_clear_and_unpoison(allocated, size);
+    if (allocator.FromPrimary(allocated))
+      __msan_clear_and_unpoison(allocated, size);
+    else
+      __msan_unpoison(allocated, size);  // Mem is already zeroed.
   } else if (flags()->poison_in_malloc) {
     __msan_poison(allocated, size);
     if (__msan_get_track_origins()) {
@@ -215,8 +218,9 @@
   uptr size = meta->requested_size;
   meta->requested_size = 0;
   // This memory will not be reused by anyone else, so we are free to keep it
-  // poisoned.
-  if (flags()->poison_in_free) {
+  // poisoned. The secondary allocator will unmap and unpoison by
+  // MsanMapUnmapCallback, no need to poison it here.
+  if (flags()->poison_in_free && allocator.FromPrimary(p)) {
     __msan_poison(p, size);
     if (__msan_get_track_origins()) {
       stack->tag = StackTrace::TAG_DEALLOC;
diff --git a/compiler-rt/test/sanitizer_common/TestCases/Posix/huge_malloc.c b/compiler-rt/test/sanitizer_common/TestCases/Posix/huge_malloc.c
--- a/compiler-rt/test/sanitizer_common/TestCases/Posix/huge_malloc.c
+++ b/compiler-rt/test/sanitizer_common/TestCases/Posix/huge_malloc.c
@@ -9,9 +9,6 @@
 // FIXME: Hangs.
 // UNSUPPORTED: tsan
 
-// FIXME: Make it work. Don't xfail to avoid excessive memory usage.
-// UNSUPPORTED: msan
-
 // Hwasan requires tagging of new allocations, so needs RSS for shadow.
 // UNSUPPORTED: hwasan
 
@@ -19,8 +16,9 @@
 
 int main(int argc, char **argv) {
   for (int i = 0; i < sizeof(void *) * 8; ++i) {
-    p = malloc(1ull << i);
-    fprintf(stderr, "%llu: %p\n", (1ull << i), p);
+    // Calloc avoids MSAN shadow poisoning.
+    p = calloc(1ull << i, 1);
+    fprintf(stderr, "%d %llu: %p\n", i, (1ull << i), p);
     free(p);
   }
   return 0;