# define PERL_VARIANTS_WORD_MASK 0x80808080
# define PERL_WORD_BOUNDARY_MASK 0x3
# elif PERL_WORDSIZE == 8
-# define PERL_VARIANTS_WORD_MASK 0x8080808080808080
+# define PERL_VARIANTS_WORD_MASK UINT64_C(0x8080808080808080)
# define PERL_WORD_BOUNDARY_MASK 0x7
# else
# error Unexpected word size