diff --git a/mpint.c b/mpint.c
index 34805d81..3e0ab530 100644
--- a/mpint.c
+++ b/mpint.c
@@ -758,7 +758,7 @@ static BignumCarry mp_add_masked_integer_into(
     for (size_t i = 0; i < rw; i++) {
         BignumInt aword = mp_word(a, i);
         size_t shift = i * BIGNUM_INT_BITS;
-        BignumInt bword = shift < BIGNUM_INT_BYTES ? b >> shift : 0;
+        BignumInt bword = shift < CHAR_BIT*sizeof(b) ? b >> shift : 0;
         BignumInt out;
         bword = (bword ^ b_xor) & b_and;
         BignumADC(out, carry, aword, bword, carry);
@@ -799,7 +799,8 @@ static void mp_add_integer_into_shifted_by_words(
          * shift n down. If it's 0, we add zero bits into r, and
          * leave n alone. */
         BignumInt bword = n & -(BignumInt)indicator;
-        uintmax_t new_n = (BIGNUM_INT_BITS < 64 ? n >> BIGNUM_INT_BITS : 0);
+        uintmax_t new_n = (BIGNUM_INT_BYTES < sizeof(n) ?
+                           n >> BIGNUM_INT_BITS : 0);
         n ^= (n ^ new_n) & -(uintmax_t)indicator;
 
         BignumInt aword = mp_word(a, i);
diff --git a/test/cryptsuite.py b/test/cryptsuite.py
index 60fc8cc5..7638d346 100755
--- a/test/cryptsuite.py
+++ b/test/cryptsuite.py
@@ -335,6 +335,22 @@ class mpint(MyTestBase):
         bm = mp_copy(bi)
         self.assertEqual(int(mp_mul(am, bm)), ai * bi)
 
+    def testAddInteger(self):
+        initial = mp_copy(4444444444444444444444444)
+
+        x = mp_new(mp_max_bits(initial) + 64)
+
+        # mp_{add,sub}_integer_into should be able to cope with any
+        # uintmax_t. Test a number that requires more than 32 bits.
+        mp_add_integer_into(x, initial, 123123123123123)
+        self.assertEqual(int(x), 4444444444567567567567567)
+        mp_sub_integer_into(x, initial, 123123123123123)
+        self.assertEqual(int(x), 4444444444321321321321321)
+
+        # mp_mul_integer_into only takes a uint16_t integer input
+        mp_mul_integer_into(x, initial, 10001)
+        self.assertEqual(int(x), 44448888888888888888888884444)
+
     def testDivision(self):
         divisors = [1, 2, 3, 2**16+1, 2**32-1, 2**32+1, 2**128-159,
                     141421356237309504880168872420969807856967187537694807]