diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index a2999b3bf77..005440eb392 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -98,6 +98,12 @@
  */
 #define SKIP_PAGES_THRESHOLD	((BlockNumber) 32)
 
+/*
+ * Size of the prefetch window for lazy vacuum backwards truncation scan.
+ * Needs to be a power of 2.
+ */
+#define PREFETCH_SIZE			((BlockNumber) 32)
+
 typedef struct LVRelStats
 {
 	/* hasindex = true means two-pass strategy; false means one-pass */
@@ -1826,13 +1832,22 @@ static BlockNumber
 count_nondeletable_pages(Relation onerel, LVRelStats *vacrelstats)
 {
 	BlockNumber blkno;
+	BlockNumber prefetchedUntil;
 	instr_time	starttime;
 
 	/* Initialize the starttime if we check for conflicting lock requests */
 	INSTR_TIME_SET_CURRENT(starttime);
 
-	/* Strange coding of loop control is needed because blkno is unsigned */
+	/*
+	 * Start checking blocks at what we believe relation end to be and move
+	 * backwards.  (Strange coding of loop control is needed because blkno is
+	 * unsigned.)  To make the scan faster, we prefetch a few blocks at a time
+	 * in forward direction, so that OS-level readahead can kick in.
+	 */
 	blkno = vacrelstats->rel_pages;
+	StaticAssertStmt((PREFETCH_SIZE & (PREFETCH_SIZE - 1)) == 0,
+					 "prefetch size must be power of 2");
+	prefetchedUntil = InvalidBlockNumber;
 	while (blkno > vacrelstats->nonempty_pages)
 	{
 		Buffer		buf;
@@ -1882,6 +1897,21 @@ count_nondeletable_pages(Relation onerel, LVRelStats *vacrelstats)
 
 		blkno--;
 
+		/* If we haven't prefetched this lot yet, do so now. */
+		if (prefetchedUntil > blkno)
+		{
+			BlockNumber	prefetchStart;
+			BlockNumber	pblkno;
+
+			prefetchStart = blkno & ~(PREFETCH_SIZE - 1);
+			for (pblkno = prefetchStart; pblkno <= blkno; pblkno++)
+			{
+				PrefetchBuffer(onerel, MAIN_FORKNUM, pblkno);
+				CHECK_FOR_INTERRUPTS();
+			}
+			prefetchedUntil = prefetchStart;
+		}
+
 		buf = ReadBufferExtended(onerel, MAIN_FORKNUM, blkno,
 								 RBM_NORMAL, vac_strategy);