LLP64 indicates a windows environment as of [1] the only architecture using a LLP64 data model is windows [1]: https://en.wikipedia.org/wiki/64-bit_computing
diff --git a/tommath.h b/tommath.h
index 5523ad0..0119906 100644
--- a/tommath.h
+++ b/tommath.h
@@ -27,7 +27,7 @@ extern "C" {
#endif
/* MS Visual C++ doesn't have a 128bit type for words, so fall back to 32bit MPI's (where words are 64bit) */
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) || defined(__LLP64__)
# define MP_32BIT
#endif