diff --git a/build/clang-plugin/tests/TestCustomHeap.cpp b/build/clang-plugin/tests/TestCustomHeap.cpp
index ec2d51ebaf5a5..c1e82f2fa7b5d 100644
--- a/build/clang-plugin/tests/TestCustomHeap.cpp
+++ b/build/clang-plugin/tests/TestCustomHeap.cpp
@@ -1,9 +1,11 @@
 #define MOZ_NONHEAP_CLASS __attribute__((annotate("moz_nonheap_class")))
+#ifndef MOZ_HEAP_ALLOCATOR
 #define MOZ_HEAP_ALLOCATOR \
   _Pragma("GCC diagnostic push") \
   _Pragma("GCC diagnostic ignored \"-Wgcc-compat\"") \
   __attribute__((annotate("moz_heap_allocator"))) \
   _Pragma("GCC diagnostic pop")
+#endif
 
 #include <stdlib.h>
 #include <memory>
diff --git a/mfbt/Char16.h b/mfbt/Char16.h
index 3c2f254aa9dbb..3d129332b43a5 100644
--- a/mfbt/Char16.h
+++ b/mfbt/Char16.h
@@ -20,6 +20,7 @@
 #ifdef WIN32
 # define MOZ_USE_CHAR16_WRAPPER
 # include <cstdint>
+# include "mozilla/Attributes.h"
   /**
    * Win32 API extensively uses wchar_t, which is represented by a separated
    * builtin type than char16_t per spec. It's not the case for MSVC prior to
@@ -39,13 +40,13 @@ class char16ptr_t
                 "char16_t and wchar_t sizes differ");
 
 public:
-  char16ptr_t(const char16_t* aPtr) : mPtr(aPtr) {}
-  char16ptr_t(const wchar_t* aPtr) :
+  MOZ_IMPLICIT char16ptr_t(const char16_t* aPtr) : mPtr(aPtr) {}
+  MOZ_IMPLICIT char16ptr_t(const wchar_t* aPtr) :
     mPtr(reinterpret_cast<const char16_t*>(aPtr))
   {}
 
   /* Without this, nullptr assignment would be ambiguous. */
-  constexpr char16ptr_t(decltype(nullptr)) : mPtr(nullptr) {}
+  constexpr MOZ_IMPLICIT char16ptr_t(decltype(nullptr)) : mPtr(nullptr) {}
 
   operator const char16_t*() const
   {
@@ -59,7 +60,7 @@ class char16ptr_t
   {
     return mPtr;
   }
-  operator bool() const
+  MOZ_IMPLICIT operator bool() const
   {
     return mPtr != nullptr;
   }