diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index 7d312cacc9..f426e6450d 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -5150,6 +5150,8 @@ int mbedtls_ecp_mod_p256_raw(mbedtls_mpi_uint *X, size_t X_limbs)
 
     RESET;
 
+    /* Use 2^224 * (2^32 - 1) + 2^192 + 2^96 - 1
+     * to modulo reduce the final carry. */
     ADD_LAST; NEXT;                                             // A0
     ;         NEXT;                                             // A1
     ;         NEXT;                                             // A2
@@ -5161,6 +5163,8 @@ int mbedtls_ecp_mod_p256_raw(mbedtls_mpi_uint *X, size_t X_limbs)
 
     RESET;
 
+    /* Use 2^224 * (2^32 - 1) + 2^192 + 2^96 - 1
+     * to modulo reduce the carry generated by the previous reduction. */
     ADD_LAST; NEXT;                                             // A0
     ;         NEXT;                                             // A1
     ;         NEXT;                                             // A2
diff --git a/scripts/mbedtls_dev/ecp.py b/scripts/mbedtls_dev/ecp.py
index f448925abe..e245171008 100644
--- a/scripts/mbedtls_dev/ecp.py
+++ b/scripts/mbedtls_dev/ecp.py
@@ -147,7 +147,7 @@ class EcpP224R1Raw(bignum_common.ModOperationCommon,
 
 class EcpP256R1Raw(bignum_common.ModOperationCommon,
                    EcpTarget):
-    """Test cases for ecp quasi_reduction()."""
+    """Test cases for ECP P256 fast reduction."""
     symbol = "-"
     test_function = "ecp_mod_p256_raw"
     test_name = "ecp_mod_p256_raw"