diff --git a/test/bntest.c b/test/bntest.c
index 2f51aaab27..8c090eeb0b 100644
--- a/test/bntest.c
+++ b/test/bntest.c
@@ -346,6 +346,51 @@ static int test_modexp_mont5()
         return 0;
     }
 
+    /* Regression test for carry bug in sqr[x]8x_mont */
+    BN_hex2bn(&n,
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000000000FFFFFFFF00"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "00000000000000000000000000000000000000000000000000FFFFFFFFFFFFFF");
+    BN_hex2bn(&a,
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000000000FFFFFFFF0000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "0000000000000000000000000000000000000000000000000000000000000000"
+        "000000000000000000000000000000000000000000FFFFFFFFFFFFFF00000000");
+    b = BN_dup(a);
+    BN_MONT_CTX_set(mont, n, ctx);
+    BN_mod_mul_montgomery(c, a, a, mont, ctx);
+    BN_mod_mul_montgomery(d, a, b, mont, ctx);
+    if (BN_cmp(c, d)) {
+        fprintf(stderr, "Montgomery multiplication test failed:"
+                        " a**2 != a*a.\n");
+        return 0;
+    }
+
     /* Zero input */
     BN_bntest_rand(p, 1024, 0, 0);
     BN_zero(a);