Index: lib/Fuzzer/test/FuzzerUnittest.cpp
===================================================================
--- lib/Fuzzer/test/FuzzerUnittest.cpp
+++ lib/Fuzzer/test/FuzzerUnittest.cpp
@@ -259,7 +259,9 @@
   TestShuffleBytes(&MutationDispatcher::Mutate_ShuffleBytes, 1 << 16);
 }
 TEST(FuzzerMutate, ShuffleBytes2) {
-  TestShuffleBytes(&MutationDispatcher::Mutate, 1 << 19);
+  // The number used below is the minimum required for the test to pass using
+  // libstdc++ and libcxx.
+  TestShuffleBytes(&MutationDispatcher::Mutate, 1 << 20);
 }
 
 void TestAddWordFromDictionary(Mutator M, int NumIter) {