diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 5b31b61..39874b9 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -120,14 +120,14 @@
  *        Wrapper function for mbedtls_err_add_ext(). See that function for
  *        more details.
  */
-#define mbedtls_error_add( high, low ) \
+#define MBEDTLS_ERROR_ADD( high, low ) \
         mbedtls_error_add_ext( high, low, __FILE__, __LINE__ )
 
 /**
  * \brief Testing hook called before adding/combining two error codes together.
  *        Only used when invasive testing is enabled via MBEDTLS_TEST_HOOKS.
  */
-void (*mbedtls_test_hook_error_add)( int, int, const char *, int );
+extern void (*mbedtls_test_hook_error_add)( int, int, const char *, int );
 
 /**
  * \brief Combines a high-level and low-level error code together.
@@ -150,6 +150,9 @@
     if( *mbedtls_test_hook_error_add != NULL )
         ( *mbedtls_test_hook_error_add )( high, low, file, line );
 #endif
+    (void)file;
+    (void)line;
+
     return( high + low );
 }