diff --git a/library/x509.c b/library/x509.c
index 2a7be32..f21e9e6 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -81,18 +81,18 @@
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     if( ( end - *p ) < 1 )
-        return( MBEDTLS_ERR_X509_INVALID_SERIAL +
-                MBEDTLS_ERR_ASN1_OUT_OF_DATA );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_SERIAL,
+                MBEDTLS_ERR_ASN1_OUT_OF_DATA ) );
 
     if( **p != ( MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_PRIMITIVE | 2 ) &&
         **p !=   MBEDTLS_ASN1_INTEGER )
-        return( MBEDTLS_ERR_X509_INVALID_SERIAL +
-                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_SERIAL,
+                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) );
 
     serial->tag = *(*p)++;
 
     if( ( ret = mbedtls_asn1_get_len( p, end, &serial->len ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_SERIAL + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_SERIAL, ret ) );
 
     serial->p = *p;
     *p += serial->len;
@@ -112,7 +112,7 @@
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     if( ( ret = mbedtls_asn1_get_alg_null( p, end, alg ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     return( 0 );
 }
@@ -126,7 +126,7 @@
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     if( ( ret = mbedtls_asn1_get_alg( p, end, alg, params ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     return( 0 );
 }
@@ -151,39 +151,39 @@
 
     /* Make sure we got a SEQUENCE and setup bounds */
     if( alg->tag != ( MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) )
-        return( MBEDTLS_ERR_X509_INVALID_ALG +
-                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) );
 
     p = alg->p;
     end = p + alg->len;
 
     if( p >= end )
-        return( MBEDTLS_ERR_X509_INVALID_ALG +
-                MBEDTLS_ERR_ASN1_OUT_OF_DATA );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                MBEDTLS_ERR_ASN1_OUT_OF_DATA ) );
 
     /* Parse md_oid */
     md_oid.tag = *p;
 
     if( ( ret = mbedtls_asn1_get_tag( &p, end, &md_oid.len, MBEDTLS_ASN1_OID ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     md_oid.p = p;
     p += md_oid.len;
 
     /* Get md_alg from md_oid */
     if( ( ret = mbedtls_oid_get_md_alg( &md_oid, md_alg ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     /* Make sure params is absent of NULL */
     if( p == end )
         return( 0 );
 
     if( ( ret = mbedtls_asn1_get_tag( &p, end, &len, MBEDTLS_ASN1_NULL ) ) != 0 || len != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     if( p != end )
-        return( MBEDTLS_ERR_X509_INVALID_ALG +
-                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
 
     return( 0 );
 }
@@ -217,8 +217,8 @@
 
     /* Make sure params is a SEQUENCE and setup bounds */
     if( params->tag != ( MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) )
-        return( MBEDTLS_ERR_X509_INVALID_ALG +
-                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) );
 
     p = (unsigned char *) params->p;
     end = p + params->len;
@@ -239,14 +239,14 @@
             return( ret );
 
         if( ( ret = mbedtls_oid_get_md_alg( &alg_id, md_alg ) ) != 0 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
         if( p != end2 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG +
-                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
     }
     else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     if( p == end )
         return( 0 );
@@ -265,19 +265,19 @@
 
         /* Only MFG1 is recognised for now */
         if( MBEDTLS_OID_CMP( MBEDTLS_OID_MGF1, &alg_id ) != 0 )
-            return( MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE +
-                    MBEDTLS_ERR_OID_NOT_FOUND );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE,
+                    MBEDTLS_ERR_OID_NOT_FOUND ) );
 
         /* Parse HashAlgorithm */
         if( ( ret = x509_get_hash_alg( &alg_params, mgf_md ) ) != 0 )
             return( ret );
 
         if( p != end2 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG +
-                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
     }
     else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     if( p == end )
         return( 0 );
@@ -291,14 +291,14 @@
         end2 = p + len;
 
         if( ( ret = mbedtls_asn1_get_int( &p, end2, salt_len ) ) != 0 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
         if( p != end2 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG +
-                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
     }
     else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     if( p == end )
         return( 0 );
@@ -314,21 +314,21 @@
         end2 = p + len;
 
         if( ( ret = mbedtls_asn1_get_int( &p, end2, &trailer_field ) ) != 0 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
         if( p != end2 )
-            return( MBEDTLS_ERR_X509_INVALID_ALG +
-                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
 
         if( trailer_field != 1 )
             return( MBEDTLS_ERR_X509_INVALID_ALG );
     }
     else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
-        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG, ret ) );
 
     if( p != end )
-        return( MBEDTLS_ERR_X509_INVALID_ALG +
-                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_ALG,
+                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
 
     return( 0 );
 }
@@ -354,47 +354,47 @@
 
     if( ( ret = mbedtls_asn1_get_tag( p, end, &len,
             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_NAME + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME, ret ) );
 
     end = *p + len;
 
     if( ( end - *p ) < 1 )
-        return( MBEDTLS_ERR_X509_INVALID_NAME +
-                MBEDTLS_ERR_ASN1_OUT_OF_DATA );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME,
+                MBEDTLS_ERR_ASN1_OUT_OF_DATA ) );
 
     oid = &cur->oid;
     oid->tag = **p;
 
     if( ( ret = mbedtls_asn1_get_tag( p, end, &oid->len, MBEDTLS_ASN1_OID ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_NAME + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME, ret ) );
 
     oid->p = *p;
     *p += oid->len;
 
     if( ( end - *p ) < 1 )
-        return( MBEDTLS_ERR_X509_INVALID_NAME +
-                MBEDTLS_ERR_ASN1_OUT_OF_DATA );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME,
+                MBEDTLS_ERR_ASN1_OUT_OF_DATA ) );
 
     if( **p != MBEDTLS_ASN1_BMP_STRING && **p != MBEDTLS_ASN1_UTF8_STRING      &&
         **p != MBEDTLS_ASN1_T61_STRING && **p != MBEDTLS_ASN1_PRINTABLE_STRING &&
         **p != MBEDTLS_ASN1_IA5_STRING && **p != MBEDTLS_ASN1_UNIVERSAL_STRING &&
         **p != MBEDTLS_ASN1_BIT_STRING )
-        return( MBEDTLS_ERR_X509_INVALID_NAME +
-                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME,
+                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) );
 
     val = &cur->val;
     val->tag = *(*p)++;
 
     if( ( ret = mbedtls_asn1_get_len( p, end, &val->len ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_NAME + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME, ret ) );
 
     val->p = *p;
     *p += val->len;
 
     if( *p != end )
     {
-        return( MBEDTLS_ERR_X509_INVALID_NAME +
-                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME,
+                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ) );
     }
 
     cur->next = NULL;
@@ -440,7 +440,7 @@
          */
         if( ( ret = mbedtls_asn1_get_tag( p, end, &set_len,
                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET ) ) != 0 )
-            return( MBEDTLS_ERR_X509_INVALID_NAME + ret );
+            return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_NAME, ret ) );
 
         end_set  = *p + set_len;
 
@@ -604,8 +604,8 @@
     unsigned char tag;
 
     if( ( end - *p ) < 1 )
-        return( MBEDTLS_ERR_X509_INVALID_DATE +
-                MBEDTLS_ERR_ASN1_OUT_OF_DATA );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_DATE,
+                MBEDTLS_ERR_ASN1_OUT_OF_DATA ) );
 
     tag = **p;
 
@@ -614,14 +614,14 @@
     else if( tag == MBEDTLS_ASN1_GENERALIZED_TIME )
         year_len = 4;
     else
-        return( MBEDTLS_ERR_X509_INVALID_DATE +
-                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_DATE,
+                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) );
 
     (*p)++;
     ret = mbedtls_asn1_get_len( p, end, &len );
 
     if( ret != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_DATE + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_DATE, ret ) );
 
     return x509_parse_time( p, len, year_len, tm );
 }
@@ -633,13 +633,13 @@
     int tag_type;
 
     if( ( end - *p ) < 1 )
-        return( MBEDTLS_ERR_X509_INVALID_SIGNATURE +
-                MBEDTLS_ERR_ASN1_OUT_OF_DATA );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_SIGNATURE,
+                MBEDTLS_ERR_ASN1_OUT_OF_DATA ) );
 
     tag_type = **p;
 
     if( ( ret = mbedtls_asn1_get_bitstring_null( p, end, &len ) ) != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_SIGNATURE + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_SIGNATURE, ret ) );
 
     sig->tag = tag_type;
     sig->len = len;
@@ -663,7 +663,7 @@
         return( MBEDTLS_ERR_X509_BAD_INPUT_DATA );
 
     if( ( ret = mbedtls_oid_get_sig_alg( sig_oid, md_alg, pk_alg ) ) != 0 )
-        return( MBEDTLS_ERR_X509_UNKNOWN_SIG_ALG + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_UNKNOWN_SIG_ALG, ret ) );
 
 #if defined(MBEDTLS_X509_RSASSA_PSS_SUPPORT)
     if( *pk_alg == MBEDTLS_PK_RSASSA_PSS )
@@ -714,7 +714,7 @@
     ret = mbedtls_asn1_get_tag( p, end, &ext->len,
               MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | tag );
     if( ret != 0 )
-        return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
+        return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret ) );
 
     ext->tag = MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | tag;
     ext->p   = *p;
@@ -725,11 +725,11 @@
      */
     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( end != *p + len )
-        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 );
 }