diff --git a/include/c11log/details/fast_oss.h b/include/c11log/details/fast_oss.h
index 487fd1d0..a7e67aeb 100644
--- a/include/c11log/details/fast_oss.h
+++ b/include/c11log/details/fast_oss.h
@@ -61,7 +61,7 @@ protected:
         return ch;
     }
 private:
-    stack_buf<256> _stackbuf;
+    stack_buf<128> _stackbuf;
 };
 
 class fast_oss :public std::ostream