diff --git a/include/mbedtls/rsa.h b/include/mbedtls/rsa.h
index 15afaee..3898687 100644
--- a/include/mbedtls/rsa.h
+++ b/include/mbedtls/rsa.h
@@ -625,7 +625,7 @@
  * \param dst      Destination context
  * \param src      Source context
  *
- * \return         O on success,
+ * \return         0 on success,
  *                 MBEDTLS_ERR_MPI_ALLOC_FAILED on memory allocation failure
  */
 int mbedtls_rsa_copy( mbedtls_rsa_context *dst, const mbedtls_rsa_context *src );