diff --git a/include/mbedtls/sha256.h b/include/mbedtls/sha256.h
index c55177d..68386a5 100644
--- a/include/mbedtls/sha256.h
+++ b/include/mbedtls/sha256.h
@@ -264,6 +264,9 @@
  *                 be a writable buffer of length \c 32 Bytes.
  * \param is224    Determines which function to use. This must be
  *                 either \c 0 for SHA-256, or \c 1 for SHA-224.
+ *
+ * \return         \c 0 on success.
+ * \return         A negative error code on failure.
  */
 int mbedtls_sha256_ret( const unsigned char *input,
                         size_t ilen,