diff --git a/src/undo.c b/src/undo.c
index b913841..62963a9 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -921,7 +921,7 @@
     static int
 undo_flush(bufinfo_T *bi)
 {
-    if (bi->bi_buffer != NULL && bi->bi_used > 0)
+    if (bi->bi_buffer != NULL && bi->bi_state != NULL && bi->bi_used > 0)
     {
 	crypt_encode_inplace(bi->bi_state, bi->bi_buffer, bi->bi_used);
 	if (fwrite(bi->bi_buffer, bi->bi_used, (size_t)1, bi->bi_fp) != 1)