diff --git a/wiretap/ngsniffer.c b/wiretap/ngsniffer.c
index 9c18623504..c41da046f5 100644
--- a/wiretap/ngsniffer.c
+++ b/wiretap/ngsniffer.c
@@ -740,7 +740,11 @@ ngsniffer_open(wtap *wth, int *err, gchar **err_info)
 
 	/* We haven't allocated any uncompression buffers yet. */
 	ngsniffer->seq.buf = NULL;
+	ngsniffer->seq.nbytes = 0;
+	ngsniffer->seq.nextout = 0;
 	ngsniffer->rand.buf = NULL;
+	ngsniffer->rand.nbytes = 0;
+	ngsniffer->rand.nextout = 0;
 
 	/* Set the current file offset; the offset in the compressed file
 	   and in the uncompressed data stream currently the same. */