diff --git a/lib/backend/bdb_ro.c b/lib/backend/bdb_ro.c
index 74569cb03d..0c132412fc 100644
--- a/lib/backend/bdb_ro.c
+++ b/lib/backend/bdb_ro.c
@@ -790,6 +790,7 @@ static unsigned int bdbro_pkgdbKey(dbiIndex dbi, dbiCursor dbc)
 struct rpmdbOps_s bdbro_dbops = {
     .name       = "bdb_ro",
     .path       = "Packages",
+    .readonly   = 1,
 
     .open       = bdbro_Open,
     .close      = bdbro_Close,
diff --git a/lib/backend/db3.c b/lib/backend/db3.c
index 3e6d198ac3..5649fb8465 100644
--- a/lib/backend/db3.c
+++ b/lib/backend/db3.c
@@ -1231,7 +1231,7 @@ static rpmRC updatePackages(dbiCursor dbc, unsigned int hdrNum, DBT *hdr)
 }
 
 /* Get current header instance number or try to allocate a new one */
-static unsigned int pkgInstance(dbiIndex dbi, int alloc)
+static unsigned int pkgInstance(dbiIndex dbi, int alloc, unsigned int hdrNumIn)
 {
     unsigned int hdrNum = 0;
 
@@ -1259,6 +1259,11 @@ static unsigned int pkgInstance(dbiIndex dbi, int alloc)
 	    hdrNum = mi_offset.ui;
 	}
 
+	if (alloc && hdrNumIn) {
+	    alloc = hdrNum >= hdrNumIn ? 0 : 1;
+	    hdrNum = alloc ? hdrNumIn - 1 : hdrNumIn;
+	}
+
 	if (alloc) {
 	    /* Rather complicated "increment by one", bswapping as needed */
 	    ++hdrNum;
@@ -1296,8 +1301,8 @@ static rpmRC db3_pkgdbPut(dbiIndex dbi, dbiCursor dbc,  unsigned int *hdrNum,
     hdr.data = hdrBlob;
     hdr.size = hdrLen;
 
-    if (hnum == 0)
-	hnum = pkgInstance(dbi, 1);
+    if (hnum == 0 || (dbi->dbi_rpmdb->db_flags & RPMDB_FLAG_CONVERT) != 0)
+	hnum = pkgInstance(dbi, 1, hnum);
 
     if (hnum)
 	rc = updatePackages(dbc, hnum, &hdr);
diff --git a/lib/backend/dbi.c b/lib/backend/dbi.c
index 7841440888..d8d262f001 100644
--- a/lib/backend/dbi.c
+++ b/lib/backend/dbi.c
@@ -57,45 +57,71 @@ dbDetectBackend(rpmdb rdb)
     const char *dbhome = rpmdbHome(rdb);
     char *db_backend = rpmExpand("%{?_db_backend}", NULL);
     char *path = NULL;
-    const struct rpmdbOps_s **ops;
+    const struct rpmdbOps_s **ops, *ops_config;
 
-    for (ops = backends; ops && *ops; ops++) {
+    rdb->db_ops = NULL;
+
+    ops_config = NULL;
+    for (ops = backends; *ops; ops++) {
 	if (rstreq(db_backend, (*ops)->name)) {
-	    rdb->db_ops = *ops;
+	    ops_config = *ops;
 	    break;
 	}
     }
 
-    for (ops = backends; ops && *ops; ops++) {
-	int stop = 0;
-	if ((*ops)->path == NULL)
-	    continue;
-
-	path = rstrscat(NULL, dbhome, "/", (*ops)->path, NULL);
-	if (access(path, F_OK) == 0 && rdb->db_ops != *ops) {
-	    rpmlog(RPMLOG_WARNING,
-		_("Found %s %s database while attempting %s backend: "
-		"using %s backend.\n"),
-		(*ops)->name, (*ops)->path, db_backend, (*ops)->name);
-	    rdb->db_ops = *ops;
-	    stop = 1;
-	}
+    /* if we have a configured backend, check it first */
+    if (ops_config && ops_config->path) {
+	path = rstrscat(NULL, dbhome, "/", ops_config->path, NULL);
+	if (access(path, F_OK) == 0)
+	    rdb->db_ops = ops_config;
 	free(path);
-	if (stop)
-	    break;
     }
 
+    /* if it did not match, check all available backends */
+    if (rdb->db_ops == NULL) {
+	for (ops = backends; *ops; ops++) {
+	    if ((*ops)->path == NULL || *ops == ops_config)
+		continue;
+
+	    path = rstrscat(NULL, dbhome, "/", (*ops)->path, NULL);
+	    if (access(path, F_OK) == 0) {
+		rpmlog(RPMLOG_WARNING,
+		    _("Found %s %s database while attempting %s backend: "
+		    "using %s backend.\n"),
+		    (*ops)->name, (*ops)->path, db_backend, (*ops)->name);
+		rdb->db_ops = *ops;
+	    }
+	    free(path);
+	    if (rdb->db_ops != NULL)
+		break;
+	}
+    }
+
+    /* if we did not find a match, use the configured backend */
+    if (rdb->db_ops == NULL && ops_config)
+	rdb->db_ops = ops_config;
+
+    /* if everything failed fall back to dummydb */
     if (rdb->db_ops == NULL) {
 	rdb->db_ops = &dummydb_dbops;
 	rpmlog(RPMLOG_WARNING, "using dummy database, installs not possible\n");
     }
 
     rdb->db_descr = rdb->db_ops->name;
+    rdb->db_ops_config = ops_config;
 
     if (db_backend)
 	free(db_backend);
 }
 
+int dbiNeedConversion(rpmdb rdb)
+{
+    if (!rdb->db_ops)
+	dbDetectBackend(rdb);
+    return rdb->db_ops->readonly && rdb->db_ops_config
+	&& rdb->db_ops_config->path && !rdb->db_ops_config->readonly;
+}
+
 const char * dbiName(dbiIndex dbi)
 {
     return dbi->dbi_file;
diff --git a/lib/backend/dbi.h b/lib/backend/dbi.h
index c4bf387870..a9584d6e23 100644
--- a/lib/backend/dbi.h
+++ b/lib/backend/dbi.h
@@ -10,6 +10,7 @@ enum rpmdbFlags {
     RPMDB_FLAG_JUSTCHECK	= (1 << 0),
     RPMDB_FLAG_REBUILD		= (1 << 1),
     RPMDB_FLAG_VERIFYONLY	= (1 << 2),
+    RPMDB_FLAG_CONVERT		= (1 << 3),
 };
 
 typedef enum dbCtrlOp_e {
@@ -60,6 +61,7 @@ struct rpmdb_s {
     int		db_buildindex;	/*!< Index rebuild indicator */
 
     const struct rpmdbOps_s * db_ops;	/*!< backend ops */
+    const struct rpmdbOps_s * db_ops_config;	/*!< configured backend ops */
 
     /* dbenv and related parameters */
     void * db_dbenv;		/*!< Backend private handle */
@@ -204,6 +206,14 @@ int dbiFlags(dbiIndex dbi);
 RPM_GNUC_INTERNAL
 const char * dbiName(dbiIndex dbi);
 
+/** \ingroup dbi
+ * Check if the database needs to be converted to a different format
+ * @param db           rpm database
+ * @return             boolean
+ */
+RPM_GNUC_INTERNAL
+int dbiNeedConversion(rpmdb rdb);
+
 /** \ingroup dbi
  * Open a database cursor.
  * @param dbi		index database handle
@@ -248,6 +258,7 @@ const void * idxdbKey(dbiIndex dbi, dbiCursor dbc, unsigned int *keylen);
 struct rpmdbOps_s {
     const char *name; /* backend name */
     const char *path; /* main database name */
+    int readonly;     /* cannot modify database */
 
     int (*open)(rpmdb rdb, rpmDbiTagVal rpmtag, dbiIndex * dbip, int flags);
     int (*close)(dbiIndex dbi, unsigned int flags);
diff --git a/lib/backend/lmdb.c b/lib/backend/lmdb.c
index f5b94ce487..b51a6ed2e1 100644
--- a/lib/backend/lmdb.c
+++ b/lib/backend/lmdb.c
@@ -804,7 +804,7 @@ static rpmRC updatePackages(dbiCursor dbc, unsigned int hdrNum, MDB_val *hdr)
 }
 
 /* Get current header instance number or try to allocate a new one */
-static unsigned int pkgInstance(dbiCursor dbc, int alloc)
+static unsigned int pkgInstance(dbiCursor dbc, int alloc, unsigned int hdrNumIn)
 {
     unsigned int hdrNum = 0;
 
@@ -826,6 +826,11 @@ static unsigned int pkgInstance(dbiCursor dbc, int alloc)
 	hdrNum = mi_offset.ui;
     }
 
+    if (alloc && hdrNumIn) {
+	alloc = hdrNum >= hdrNumIn ? 0 : 1;
+	hdrNum = alloc ? hdrNumIn - 1 : hdrNumIn;
+    }
+
     if (alloc) {
 	/* Rather complicated "increment by one", bswapping as needed */
 	++hdrNum;
@@ -856,8 +861,8 @@ static rpmRC lmdb_pkgdbPut(dbiIndex dbi, dbiCursor dbc,  unsigned int *hdrNum,
     hdr.mv_data = hdrBlob;
     hdr.mv_size = hdrLen;
 
-    if (hnum == 0)
-	hnum = pkgInstance(dbc, 1);
+    if (hnum == 0 || (dbi->dbi_rpmdb->db_flags & RPMDB_FLAG_CONVERT) != 0)
+	hnum = pkgInstance(dbc, 1, hnum);
 
     if (hnum)
 	rc = updatePackages(dbc, hnum, &hdr);
diff --git a/lib/backend/ndb/rpmpkg.c b/lib/backend/ndb/rpmpkg.c
index 922ae110bd..387e37cb56 100644
--- a/lib/backend/ndb/rpmpkg.c
+++ b/lib/backend/ndb/rpmpkg.c
@@ -968,11 +968,12 @@ static int rpmpkgPutInternal(rpmpkgdb pkgdb, unsigned int pkgidx, unsigned char
     if (rpmpkgWriteBlob(pkgdb, pkgidx, blkoff, blkcnt, blob, blobl, pkgdb->generation)) {
 	return RPMRC_FAIL;
     }
+    /* update nextpkgidx if needed */
+    if (pkgidx >= pkgdb->nextpkgidx) {
+	pkgdb->nextpkgidx = pkgidx + 1;
+    }
     /* write slot */
     slotno = oldslot ? oldslot->slotno : pkgdb->freeslot;
-    if (!slotno) {
-	return RPMRC_FAIL;
-    }
     if (rpmpkgWriteslot(pkgdb, slotno, pkgidx, blkoff, blkcnt)) {
 	free(pkgdb->slots);
 	pkgdb->slots = 0;
diff --git a/lib/rpmdb.c b/lib/rpmdb.c
index 91543eb686..7c9b64b66d 100644
--- a/lib/rpmdb.c
+++ b/lib/rpmdb.c
@@ -505,8 +505,16 @@ static int openDatabase(const char * prefix,
 	    rpmsqActivate(1);
 	}
 
+	/* Convert the database if needed */
+	if (!db->db_pkgs && !justCheck && (mode & O_ACCMODE) == O_RDWR && dbiNeedConversion(db)) {
+	    rpmlog(RPMLOG_WARNING, _("Converting database from %s to %s format\n"), db->db_ops->name, db->db_ops_config->name);
+	    rc = rpmdbRebuild(prefix, NULL, NULL, RPMDB_REBUILD_FLAG_CONVERT);
+	    db->db_ops = NULL;		/* force re-detection of backend */
+	}
+
 	/* Just the primary Packages database opened here */
-	rc = pkgdbOpen(db, db->db_flags, NULL);
+	if (!rc)
+	    rc = pkgdbOpen(db, db->db_flags, NULL);
 	if (!db->db_descr)
 	    db->db_descr = "unknown db";
     }
@@ -2306,6 +2314,15 @@ int rpmdbAdd(rpmdb db, Header h)
     if (db == NULL)
 	return 0;
 
+    if ((db->db_flags & RPMDB_FLAG_CONVERT) != 0) {
+	/* keep old instance numbers when converting */
+	hdrNum = headerGetInstance(h);
+	if (hdrNum == 0) {
+	    ret = -1;
+	    goto exit;
+	}
+    }
+
     hdrBlob = headerExport(h, &hdrLen);
     if (hdrBlob == NULL || hdrLen == 0) {
 	ret = -1;
@@ -2479,7 +2496,8 @@ static int rpmdbSetPermissions(char * src, char * dest)
 }
 
 int rpmdbRebuild(const char * prefix, rpmts ts,
-		rpmRC (*hdrchk) (rpmts ts, const void *uh, size_t uc, char ** msg))
+		rpmRC (*hdrchk) (rpmts ts, const void *uh, size_t uc, char ** msg),
+		int rebuildflags)
 {
     rpmdb olddb;
     char * dbpath = NULL;
@@ -2524,7 +2542,9 @@ int rpmdbRebuild(const char * prefix, rpmts ts,
 	goto exit;
     }
     if (openDatabase(prefix, newdbpath, &newdb,
-		     (O_RDWR | O_CREAT), 0644, RPMDB_FLAG_REBUILD)) {
+		     (O_RDWR | O_CREAT), 0644, RPMDB_FLAG_REBUILD |
+		     (rebuildflags & RPMDB_REBUILD_FLAG_CONVERT ?
+		         RPMDB_FLAG_CONVERT : 0))) {
 	rc = 1;
 	goto exit;
     }
@@ -2557,6 +2577,7 @@ int rpmdbRebuild(const char * prefix, rpmts ts,
 	    /* Deleted entries are eliminated in legacy headers by copy. */
 	    if (headerIsEntry(h, RPMTAG_HEADERIMAGE)) {
 		Header nh = headerReload(headerCopy(h), RPMTAG_HEADERIMAGE);
+		headerSetInstance(nh, headerGetInstance(h));
 		rc = rpmdbAdd(newdb, nh);
 		headerFree(nh);
 	    } else {
diff --git a/lib/rpmdb_internal.h b/lib/rpmdb_internal.h
index 5ad844c719..f38382d8df 100644
--- a/lib/rpmdb_internal.h
+++ b/lib/rpmdb_internal.h
@@ -23,6 +23,10 @@ extern "C" {
 #undef HTKEYTYPE
 #undef HTDATATYPE
 
+enum rpmdbRebuildFlags_e {
+    RPMDB_REBUILD_FLAG_CONVERT	= (1 << 0),
+};
+
 /** \ingroup rpmdb
  * Reference a database instance.
  * @param db		rpm database
@@ -63,11 +67,13 @@ int rpmdbClose (rpmdb db);
  * @param prefix	path to top of install tree
  * @param ts		transaction set (or NULL)
  * @param (*hdrchk)	headerCheck() vector (or NULL)
+ * @param rebuildflags	flags
  * @return		0 on success
  */
 RPM_GNUC_INTERNAL
 int rpmdbRebuild(const char * prefix, rpmts ts,
-		rpmRC (*hdrchk) (rpmts ts, const void *uh, size_t uc, char ** msg));
+		rpmRC (*hdrchk) (rpmts ts, const void *uh, size_t uc, char ** msg),
+		int rebuildflags);
 
 /** \ingroup rpmdb
  * Verify database components.
diff --git a/lib/rpmts.c b/lib/rpmts.c
index 22c14d02c9..bec29f745e 100644
--- a/lib/rpmts.c
+++ b/lib/rpmts.c
@@ -143,9 +143,9 @@ int rpmtsRebuildDB(rpmts ts)
     txn = rpmtxnBegin(ts, RPMTXN_WRITE);
     if (txn) {
 	if (!(ts->vsflags & RPMVSF_NOHDRCHK))
-	    rc = rpmdbRebuild(ts->rootDir, ts, headerCheck);
+	    rc = rpmdbRebuild(ts->rootDir, ts, headerCheck, 0);
 	else
-	    rc = rpmdbRebuild(ts->rootDir, NULL, NULL);
+	    rc = rpmdbRebuild(ts->rootDir, NULL, NULL, 0);
 	rpmtxnEnd(txn);
     }
     return rc;