diff --git a/mercurial/thirdparty/xdiff/xprepare.c b/mercurial/thirdparty/xdiff/xprepare.c
--- a/mercurial/thirdparty/xdiff/xprepare.c
+++ b/mercurial/thirdparty/xdiff/xprepare.c
@@ -441,17 +441,27 @@
 	recs1 = xdf1->recs;
 	recs2 = xdf2->recs;
 	for (i = 0, lim = XDL_MIN(xdf1->nrec, xdf2->nrec); i < lim;
-	     i++, recs1++, recs2++)
-		if ((*recs1)->ha != (*recs2)->ha)
+	     i++, recs1++, recs2++) {
+		/* rec->ha is not processed by xdl_prepare_hashtable, so
+		 * they are not unique - do a content match here */
+		if ((*recs1)->size != (*recs2)->size)
 			break;
+		if (memcmp((*recs1)->ptr, (*recs2)->ptr, (*recs1)->size) != 0)
+			break;
+	}
 
 	xdf1->dstart = xdf2->dstart = i;
 
 	recs1 = xdf1->recs + xdf1->nrec - 1;
 	recs2 = xdf2->recs + xdf2->nrec - 1;
-	for (lim -= i, i = 0; i < lim; i++, recs1--, recs2--)
-		if ((*recs1)->ha != (*recs2)->ha)
+	for (lim -= i, i = 0; i < lim; i++, recs1--, recs2--) {
+		/* rec->ha is not processed by xdl_prepare_hashtable, so
+		 * they are not unique - do a content match here */
+		if ((*recs1)->size != (*recs2)->size)
 			break;
+		if (memcmp((*recs1)->ptr, (*recs2)->ptr, (*recs1)->size) != 0)
+			break;
+	}
 
 	xdf1->dend = xdf1->nrec - i - 1;
 	xdf2->dend = xdf2->nrec - i - 1;