--- a/js/public/RequiredDefines.h
+++ b/js/public/RequiredDefines.h
@@ -23,9 +23,12 @@
  * (INT8_C for example) used to specify a literal constant of the proper type,
  * and with __STDC_FORMAT_MACROS for the format macros (PRId32 for example) used
  * with the fprintf function family.
  */
 #define __STDC_LIMIT_MACROS
 #define __STDC_CONSTANT_MACROS
 #define __STDC_FORMAT_MACROS
 
+/* Also define a char16_t type if not provided by the compiler. */
+#include "mozilla/Char16.h"
+
 #endif /* js_RequiredDefines_h */

--- a/js/src/js-confdefs.h.in
+++ b/js/src/js-confdefs.h.in
@@ -5,11 +5,9 @@
 
 #ifndef js_confdefs_h
 #define js_confdefs_h
 
 @ALLDEFINES@
 
 #include "js/RequiredDefines.h"
 
-#include "mozilla/Char16.h"
-
 #endif /* js_confdefs_h */