diff --git a/mfbt/Assertions.h b/mfbt/Assertions.h
index 2690160e72e5..14d31f4a6298 100644
--- a/mfbt/Assertions.h
+++ b/mfbt/Assertions.h
@@ -66,12 +66,6 @@ MOZ_END_EXTERN_C
 #  include <android/log.h>
 #endif
 
-#if defined(__GNUC__)
-#  define MOZ_UNUSED_ATTRIBUTE __attribute__((unused))
-#else
-#  define MOZ_UNUSED_ATTRIBUTE /* nothing */
-#endif
-
 /*
  * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
  * In C++11, static_assert is provided by the compiler to the same effect.
@@ -96,6 +90,11 @@ MOZ_END_EXTERN_C
     * triggers compiler warnings with some versions of gcc, so mark the typedefs
     * as permissibly-unused to disable the warnings.
     */
+#  if defined(__GNUC__)
+#    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
+#  else
+#    define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
+#  endif
 #  define MOZ_STATIC_ASSERT_GLUE1(x, y)          x##y
 #  define MOZ_STATIC_ASSERT_GLUE(x, y)           MOZ_STATIC_ASSERT_GLUE1(x, y)
 #  if defined(__SUNPRO_CC)
@@ -128,10 +127,10 @@ MOZ_END_EXTERN_C
       * code.
       */
 #    define MOZ_STATIC_ASSERT(cond, reason) \
-       typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_UNUSED_ATTRIBUTE
+       typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 #  else
 #    define MOZ_STATIC_ASSERT(cond, reason) \
-       extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_UNUSED_ATTRIBUTE
+       extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
 #  endif
 
 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason)  MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
diff --git a/toolkit/xre/nsNativeAppSupportWin.cpp b/toolkit/xre/nsNativeAppSupportWin.cpp
index b25df30e1ef2..530c264d81a9 100644
--- a/toolkit/xre/nsNativeAppSupportWin.cpp
+++ b/toolkit/xre/nsNativeAppSupportWin.cpp
@@ -110,7 +110,7 @@ struct Win32Mutex {
             // Make sure we release it if we own it.
             Unlock();
 
-            BOOL rc MOZ_UNUSED_ATTRIBUTE = CloseHandle( mHandle );
+            BOOL rc MOZ_MAYBE_UNUSED = CloseHandle( mHandle );
 #if MOZ_DEBUG_DDE
             if ( !rc ) {
                 printf( "CloseHandle error = 0x%08X\n", (int)GetLastError() );