diff --git a/ext/celt/gstceltenc.c b/ext/celt/gstceltenc.c
index 9e6944df0f..1413caac3f 100644
--- a/ext/celt/gstceltenc.c
+++ b/ext/celt/gstceltenc.c
@@ -820,7 +820,7 @@ gst_celt_enc_encode (GstCeltEnc * enc, gboolean flush)
   }
 
   if (flush && gst_adapter_available (enc->adapter) % bytes != 0) {
-    guint diff = gst_adapter_available (enc->adapter) % bytes;
+    guint diff = bytes - gst_adapter_available (enc->adapter) % bytes;
     GstBuffer *buf = gst_buffer_new_and_alloc (diff);
 
     memset (GST_BUFFER_DATA (buf), 0, diff);