diff --git a/library/pk.c b/library/pk.c
index 1ded487..c647b45 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -1401,8 +1401,7 @@
         mbedtls_ecp_keypair *ec = mbedtls_pk_ec_rw(*pk);
         int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
-        d_len = PSA_BITS_TO_BYTES(ec->grp.nbits);
-        if ((ret = mbedtls_ecp_write_key(ec, d, d_len)) != 0) {
+        if ((ret = mbedtls_ecp_write_key_ext(ec, &d_len, d, sizeof(d))) != 0) {
             return ret;
         }
 
diff --git a/library/pkwrite.c b/library/pkwrite.c
index b9ddcf1..5e009c5 100644
--- a/library/pkwrite.c
+++ b/library/pkwrite.c
@@ -202,7 +202,7 @@
         mbedtls_ecp_keypair *ec = mbedtls_pk_ec_rw(*pk);
         byte_length = (ec->grp.pbits + 7) / 8;
 
-        ret = mbedtls_ecp_write_key(ec, tmp, byte_length);
+        ret = mbedtls_ecp_write_key_ext(ec, &byte_length, tmp, sizeof(tmp));
         if (ret != 0) {
             goto exit;
         }
diff --git a/library/psa_crypto_ecp.c b/library/psa_crypto_ecp.c
index 7edea81..e373ad9 100644
--- a/library/psa_crypto_ecp.c
+++ b/library/psa_crypto_ecp.c
@@ -281,20 +281,8 @@
 
         return status;
     } else {
-        if (data_size < PSA_BITS_TO_BYTES(ecp->grp.nbits)) {
-            return PSA_ERROR_BUFFER_TOO_SMALL;
-        }
-
         status = mbedtls_to_psa_error(
-            mbedtls_ecp_write_key(ecp,
-                                  data,
-                                  PSA_BITS_TO_BYTES(ecp->grp.nbits)));
-        if (status == PSA_SUCCESS) {
-            *data_length = PSA_BITS_TO_BYTES(ecp->grp.nbits);
-        } else {
-            memset(data, 0, data_size);
-        }
-
+            mbedtls_ecp_write_key_ext(ecp, data_length, data, data_size));
         return status;
     }
 }
@@ -359,14 +347,11 @@
     }
 
     status = mbedtls_to_psa_error(
-        mbedtls_ecp_write_key(&ecp, key_buffer, key_buffer_size));
+        mbedtls_ecp_write_key_ext(&ecp, key_buffer_length,
+                                  key_buffer, key_buffer_size));
 
     mbedtls_ecp_keypair_free(&ecp);
 
-    if (status == PSA_SUCCESS) {
-        *key_buffer_length = key_buffer_size;
-    }
-
     return status;
 }
 #endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_GENERATE */
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index 53a9ce2..5bee188 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -2703,8 +2703,7 @@
                              PSA_KEY_TYPE_ECC_KEY_PAIR(ssl->handshake->xxdh_psa_type));
             psa_set_key_bits(&key_attributes, ssl->handshake->xxdh_psa_bits);
 
-            key_len = PSA_BITS_TO_BYTES(key->grp.pbits);
-            ret = mbedtls_ecp_write_key(key, buf, key_len);
+            ret = mbedtls_ecp_write_key_ext(key, &key_len, buf, sizeof(buf));
             if (ret != 0) {
                 mbedtls_platform_zeroize(buf, sizeof(buf));
                 break;