diff --git a/artiq/firmware/ksupport/glue.c b/artiq/firmware/ksupport/glue.c
index 0a6cd3eea..807ad563e 100644
--- a/artiq/firmware/ksupport/glue.c
+++ b/artiq/firmware/ksupport/glue.c
@@ -38,6 +38,11 @@ int fprintf(FILE *stream, const char *fmt, ...)
     return 0;
 }
 
+/* called by libunwind */
+int fflush(FILE *stream)
+{
+}
+
 /* called by libunwind */
 int dladdr (const void *address, Dl_info *info)
 {