--- a/parser/expat/expat_config.h
+++ b/parser/expat/expat_config.h
@@ -22,20 +22,29 @@
 /* Other Mozilla code relies on memmove already, so we assume it's available */
 #define HAVE_MEMMOVE 1
 
 #define XMLCALL
 #define XML_STATIC
 #define XMLIMPORT
 
 #define XML_UNICODE
+typedef char XML_LChar;
+/*
+ * The char16_t type is only usable in C++ code, so we need this ugly hack to
+ * select a binary compatible C type for the expat C code to use.
+ */
+#ifdef __cplusplus
 typedef char16_t XML_Char;
-typedef char XML_LChar;
 #define XML_T(x) (char16_t)x
-#define XML_L(x) x
+#else
+#include <stdint.h>
+typedef uint16_t XML_Char;
+#define XML_T(x) (uint16_t)x
+#endif
 
 #define XML_DTD
 #define XML_NS
 
 /* avoid conflicts with system version of libexpat */
 
 /* expat.h */
 #define XML_SetElementDeclHandler MOZ_XML_SetElementDeclHandler