diff --git a/library/x509_csr.c b/library/x509_csr.c
index 1f133e8..1ea77fe 100644
--- a/library/x509_csr.c
+++ b/library/x509_csr.c
@@ -78,7 +78,6 @@
     int ret;
     size_t len;
     unsigned char *end_ext_data;
-
     while (*p < end) {
         mbedtls_x509_buf extn_oid = { 0, 0, NULL };
         int ext_type = 0;
@@ -86,7 +85,7 @@
         /* Read sequence tag */
         if ((ret = mbedtls_asn1_get_tag(p, end, &len,
                                         MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) != 0) {
-            return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
         }
 
         end_ext_data = *p + len;
@@ -94,7 +93,7 @@
         /* Get extension ID */
         if ((ret = mbedtls_asn1_get_tag(p, end_ext_data, &extn_oid.len,
                                         MBEDTLS_ASN1_OID)) != 0) {
-            return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
         }
 
         extn_oid.tag = MBEDTLS_ASN1_OID;
@@ -104,11 +103,12 @@
         /* Data should be octet string type */
         if ((ret = mbedtls_asn1_get_tag(p, end_ext_data, &len,
                                         MBEDTLS_ASN1_OCTET_STRING)) != 0) {
-            return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
         }
+
         if (*p + len != end_ext_data) {
-            return MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
-                   MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                     MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
         }
 
         /*
@@ -116,49 +116,54 @@
          */
         ret = mbedtls_oid_get_x509_ext_type(&extn_oid, &ext_type);
 
-        if (ret == 0) {
-            /* Forbid repeated extensions */
-            if ((csr->ext_types & ext_type) != 0) {
-                return MBEDTLS_ERR_X509_INVALID_EXTENSIONS;
-            }
+        if (ret != 0) {
+            *p = end_ext_data;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                     ret);
+        }
 
-            csr->ext_types |= ext_type;
+        /* Forbid repeated extensions */
+        if ((csr->ext_types & ext_type) != 0) {
+            return (MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                      MBEDTLS_ERR_ASN1_INVALID_DATA));
+        }
 
-            switch (ext_type) {
-                case MBEDTLS_X509_EXT_KEY_USAGE:
-                    /* Parse key usage */
-                    if ((ret = mbedtls_x509_get_key_usage(p, end_ext_data,
-                                                          &csr->key_usage)) != 0) {
-                        return ret;
-                    }
-                    break;
+        csr->ext_types |= ext_type;
 
-                case MBEDTLS_X509_EXT_SUBJECT_ALT_NAME:
-                    /* Parse subject alt name */
-                    if ((ret = mbedtls_x509_get_subject_alt_name(p, end_ext_data,
-                                                                 &csr->subject_alt_names)) != 0) {
-                        return ret;
-                    }
-                    break;
+        switch (ext_type) {
+            case MBEDTLS_X509_EXT_KEY_USAGE:
+                /* Parse key usage */
+                if ((ret = mbedtls_x509_get_key_usage(p, end_ext_data,
+                                                        &csr->key_usage)) != 0) {
+                    return ret;
+                }
+                break;
 
-                case MBEDTLS_X509_EXT_NS_CERT_TYPE:
-                    /* Parse netscape certificate type */
-                    if ((ret = mbedtls_x509_get_ns_cert_type(p, end_ext_data,
-                                                             &csr->ns_cert_type)) != 0) {
-                        return ret;
-                    }
-                    break;
-                default:
-                    break;
-            }
+            case MBEDTLS_X509_EXT_SUBJECT_ALT_NAME:
+                /* Parse subject alt name */
+                if ((ret = mbedtls_x509_get_subject_alt_name(p, end_ext_data,
+                                                                &csr->subject_alt_names)) != 0) {
+                    return ret;
+                }
+                break;
+
+            case MBEDTLS_X509_EXT_NS_CERT_TYPE:
+                /* Parse netscape certificate type */
+                if ((ret = mbedtls_x509_get_ns_cert_type(p, end_ext_data,
+                                                            &csr->ns_cert_type)) != 0) {
+                    return ret;
+                }
+                break;
+            default:
+                break;
         }
 
         *p = end_ext_data;
     }
 
     if (*p != end) {
-        return MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
-               MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
+        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                 MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
     }
 
     return 0;
@@ -180,14 +185,14 @@
 
         if ((ret = mbedtls_asn1_get_tag(p, end, &len,
                                         MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) != 0) {
-            return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
         }
         end_attr_data = *p + len;
 
         /* Get attribute ID */
         if ((ret = mbedtls_asn1_get_tag(p, end_attr_data, &attr_oid.len,
                                         MBEDTLS_ASN1_OID)) != 0) {
-            return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
         }
 
         attr_oid.tag = MBEDTLS_ASN1_OID;
@@ -196,24 +201,25 @@
 
         /* Check that this is an extension-request attribute */
         if (MBEDTLS_OID_CMP(MBEDTLS_OID_PKCS9_CSR_EXT_REQ, &attr_oid) == 0) {
+
             if ((ret = mbedtls_asn1_get_tag(p, end, &len,
                                             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET)) != 0) {
-                return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+                return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
             }
 
             if ((ret = mbedtls_asn1_get_tag(p, end, &len,
                                             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) !=
                 0) {
-                return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+                return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
             }
 
             if ((ret = x509_csr_parse_extensions(csr, p, *p + len)) != 0) {
-                return MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret;
+                return ret;
             }
 
             if (*p != end_attr_data) {
-                return MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
-                       MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
+                return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                         MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
             }
         }
 
@@ -221,8 +227,8 @@
     }
 
     if (*p != end) {
-        return MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
-               MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
+        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
     }
 
     return 0;