diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index 40db15a..7a74a1f 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -481,7 +481,7 @@
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
 
     c2 -= len;
-    memcpy( c2, c, len );
+    mbedtls_platform_memcpy( c2, c, len );
 
     len += sig_and_oid_len;
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );