diff --git a/library/error.c b/library/error.c
index 901a369..4e279b0 100644
--- a/library/error.c
+++ b/library/error.c
@@ -893,6 +893,22 @@
     return( NULL );
 }
 
+#if defined(MBEDTLS_TEST_HOOKS)
+static void (*err_add_hook)( int, int, const char *, int );
+
+void mbedtls_set_err_add_hook(void *hook)
+{
+    err_add_hook = hook;
+}
+
+int mbedtls_err_add( int high, int low, const char *file, int line )
+{
+    if( err_add_hook != NULL )
+        (*err_add_hook)( high, low, file, line );
+    return ( high + low );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
+
 void mbedtls_strerror( int ret, char *buf, size_t buflen )
 {
     size_t len;