diff --git a/wolfcrypt/src/sp_int.c b/wolfcrypt/src/sp_int.c
index 30d3d01a8..c20085c87 100644
--- a/wolfcrypt/src/sp_int.c
+++ b/wolfcrypt/src/sp_int.c
@@ -11991,7 +11991,8 @@ static int _sp_mont_red(sp_int* a, sp_int* m, sp_int_digit mp)
         bits = SP_WORD_SIZE;
     }
     else {
-        sp_int_digit mask = (1UL << (bits & (SP_WORD_SIZE - 1))) - 1;
+        sp_int_digit mask = (sp_int_digit)
+                            ((1UL << (bits & (SP_WORD_SIZE - 1))) - 1);
         sp_int_word o = 0;
         w = 0;
         for (i = 0; i < m->used; i++) {