diff --git a/src/stdout.c b/src/stdout.c
index bce6a24e6..78471f55d 100644
--- a/src/stdout.c
+++ b/src/stdout.c
@@ -14,6 +14,8 @@
 
 static void out_flush (out_t *out)
 {
+  if (out->len == 0) return;
+
   fwrite (out->buf, 1, out->len, out->fp);
 
   out->len = 0;