@@ -2183,7 +2183,9 @@ _bt_readfirstpage(IndexScanDesc scan, OffsetNumber offnum, ScanDirection dir)
21832183 * scan. A seized=false caller's blkno can never be assumed to be the page
21842184 * that must be read next during a parallel scan, though. We must figure that
21852185 * part out for ourselves by seizing the scan (the correct page to read might
2186- * already be beyond the seized=false caller's blkno during a parallel scan).
2186+ * already be beyond the seized=false caller's blkno during a parallel scan,
2187+ * unless blkno/so->currPos.nextPage/so->currPos.prevPage is already P_NONE,
2188+ * or unless so->currPos.moreRight/so->currPos.moreLeft is already unset).
21872189 *
21882190 * On success exit, so->currPos is updated to contain data from the next
21892191 * interesting page, and we return true. We hold a pin on the buffer on
@@ -2204,6 +2206,7 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno,
22042206BTScanOpaque so = (BTScanOpaque )scan -> opaque ;
22052207
22062208Assert (so -> currPos .currPage == lastcurrblkno || seized );
2209+ Assert (!(blkno == P_NONE && seized ));
22072210Assert (!BTScanPosIsPinned (so -> currPos ));
22082211
22092212/*