diff --git a/test/std/numerics/rand/rand.device/ctor.pass.cpp b/test/std/numerics/rand/rand.device/ctor.pass.cpp
index 49403896a..5d72e474e 100644
--- a/test/std/numerics/rand/rand.device/ctor.pass.cpp
+++ b/test/std/numerics/rand/rand.device/ctor.pass.cpp
@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// See bugs.llvm.org/PR20183
+//
 // XFAIL: with_system_cxx_lib=macosx10.11
 // XFAIL: with_system_cxx_lib=macosx10.10
 // XFAIL: with_system_cxx_lib=macosx10.9
diff --git a/test/std/numerics/rand/rand.device/eval.pass.cpp b/test/std/numerics/rand/rand.device/eval.pass.cpp
index c6e01ac25..b34e40c75 100644
--- a/test/std/numerics/rand/rand.device/eval.pass.cpp
+++ b/test/std/numerics/rand/rand.device/eval.pass.cpp
@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// See bugs.llvm.org/PR20183
+//
 // XFAIL: with_system_cxx_lib=macosx10.11
 // XFAIL: with_system_cxx_lib=macosx10.10
 // XFAIL: with_system_cxx_lib=macosx10.9