diff --git a/examples/io.c b/examples/io.c
index fdd75e7c29c6c8f5f1bf36f3c079cc57b946b295..2cab495b9a22a50fb88596de2564d38343cefea2 100644
--- a/examples/io.c
+++ b/examples/io.c
@@ -129,7 +129,7 @@ write_string(FILE *f, unsigned size, const char *buffer)
 {
   size_t res = fwrite(buffer, 1, size, f);
 
-  return res > 0;
+  return res == size;
 }
 
 int