diff --git a/library/error.c b/library/error.c
index 901a369..b5bd8d7 100644
--- a/library/error.c
+++ b/library/error.c
@@ -893,6 +893,8 @@
     return( NULL );
 }
 
+void (*mbedtls_test_hook_error_add)( int, int, const char *, int );
+
 void mbedtls_strerror( int ret, char *buf, size_t buflen )
 {
     size_t len;