diff --git a/include/polarssl/x509write.h b/include/polarssl/x509write.h
index aa4d053..6710474 100644
--- a/include/polarssl/x509write.h
+++ b/include/polarssl/x509write.h
@@ -80,7 +80,7 @@
     rsa_context *rsa;
     x509_req_name *subject;
     md_type_t md_alg;
-    unsigned char key_usage;
+    asn1_named_data *extensions;
 }
 x509_csr;
 
@@ -131,8 +131,10 @@
  *
  * \param ctx       CSR context to use
  * \param key_usage key usage bitstring to set
+ *
+ * \return          0 if successful, or POLARSSL_ERR_X509WRITE_MALLOC_FAILED
  */
-void x509write_csr_set_key_usage( x509_csr *ctx, unsigned char key_usage );
+int x509write_csr_set_key_usage( x509_csr *ctx, unsigned char key_usage );
 
 /**
  * \brief           Free the contents of a CSR context