diff --git a/internal/fixnum.h b/internal/fixnum.h
index cdb60ee1ff..8c251adef1 100644
--- a/internal/fixnum.h
+++ b/internal/fixnum.h
@@ -18,7 +18,7 @@
 #if HAVE_LONG_LONG && SIZEOF_LONG * 2 <= SIZEOF_LONG_LONG
 # define DLONG LONG_LONG
 # define DL2NUM(x) LL2NUM(x)
-#elif defined(HAVE_INT128_T)
+#elif defined(HAVE_INT128_T) && !(defined(__OpenBSD__) && defined(__mips64__))
 # define DLONG int128_t
 # define DL2NUM(x) (RB_FIXABLE(x) ? LONG2FIX(x) : rb_int128t2big(x))
 VALUE rb_int128t2big(int128_t n); /* in bignum.c */