diff --git a/scripts/mbedtls_dev/ecp.py b/scripts/mbedtls_dev/ecp.py
index 10fcc5e475..aee8718316 100644
--- a/scripts/mbedtls_dev/ecp.py
+++ b/scripts/mbedtls_dev/ecp.py
@@ -189,6 +189,11 @@ class EcpP384R1Raw(bignum_common.ModOperationCommon,
          "285d99ae3b53da5ba36e56701e2b17c225f1239556c5f00117fa140218b46ebd8"
          "e34f50d0018701fa8a0a5cc00000000000000004410bcb4ffffffff00000000"),
 
+        # Testing the second round of carry reduction
+        ("000000000000000000000000ffffffffffffffffffffffffffffffffffffffff"
+         "ffffffffffffffff00000000000000000000000000000000ffffffff00000000"
+         "000000000000000100000000000000000000000000000000ffffffff00000001"),
+
         # First 8 number generated by random.getrandbits(768) - seed(2,2)
         ("ffed9235288bc781ae66267594c9c9500925e4749b575bd13653f8dd9b1f282e"
          "4067c3584ee207f8da94e3e8ab73738fcf1822ffbc6887782b491044d5e34124"