--- a/src/plugins/fts-flatcurve/fts-backend-flatcurve-xapian.cc
+++ b/src/plugins/fts-flatcurve/fts-backend-flatcurve-xapian.cc
@@ -1838,13 +1838,27 @@
 
 	unsigned int updates = 0;
 	for (iter = mset.begin(); iter != mset.end(); ++iter) {
-		Xapian::Document doc = iter.get_document();
 		try {
+			/* get_document() belongs inside the try: it is the
+			 * call that throws DocNotFoundError when a document
+			 * has no termlist, and this rebuild exists precisely
+			 * to salvage databases the native compact refused. */
+			Xapian::Document doc = iter.get_document();
 	                xdb->dbw->replace_document(doc.get_docid(), doc);
 			if (++updates > FLATCURVE_MANUAL_OPTIMIZE_COMMIT_LIMIT) {
 				xdb->dbw->commit();
 				updates = 0;
 			}
+		} catch (Xapian::DocNotFoundError &e) {
+			/* A document listed in the MSet whose termlist is
+			 * gone. It belongs to a message that no longer
+			 * exists, so there is nothing to carry over -- skip
+			 * it rather than abort, which would leave every shard
+			 * in place to accumulate without bound. */
+			e_debug(backend->event, "Optimize: skipping "
+				"unreadable document; %s",
+				e.get_description().c_str());
+			continue;
 	        } catch (Xapian::Error &e) {
 			*error_r = t_strdup(e.get_description().c_str());
 			return -1;