diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c
index a83c18c2a4..93cdd35fea 100644
--- a/src/backend/storage/aio/read_stream.c
+++ b/src/backend/storage/aio/read_stream.c
@@ -117,13 +117,10 @@ struct ReadStream
 	bool		advice_enabled;
 
 	/*
-	 * Small buffer of block numbers, useful for 'ungetting' to resolve flow
-	 * control problems when I/Os are split.  Also useful for batch-loading
-	 * block numbers in the fast path.
+	 * One-block buffer to support 'ungetting' a block number, to resolve flow
+	 * control problems when I/Os are split.
 	 */
-	BlockNumber blocknums[16];
-	int16		blocknums_count;
-	int16		blocknums_next;
+	BlockNumber buffered_blocknum;
 
 	/*
 	 * The callback that will tell us which block numbers to read, and an
@@ -167,23 +164,23 @@ get_per_buffer_data(ReadStream *stream, int16 buffer_index)
 }
 
 /*
- * Ask the callback which block it would like us to read next, with a small
- * buffer in front to allow read_stream_unget_block() to work and to allow the
- * fast path to skip this function and work directly from the array.
+ * Ask the callback which block it would like us to read next, with a one block
+ * buffer in front to allow read_stream_unget_block() to work.
  */
 static inline BlockNumber
 read_stream_get_block(ReadStream *stream, void *per_buffer_data)
 {
-	if (stream->blocknums_next < stream->blocknums_count)
-		return stream->blocknums[stream->blocknums_next++];
+	BlockNumber blocknum;
 
-	/*
-	 * We only bother to fetch one at a time here (but see the fast path which
-	 * uses more).
-	 */
-	return stream->callback(stream,
-							stream->callback_private_data,
-							per_buffer_data);
+	blocknum = stream->buffered_blocknum;
+	if (blocknum != InvalidBlockNumber)
+		stream->buffered_blocknum = InvalidBlockNumber;
+	else
+		blocknum = stream->callback(stream,
+									stream->callback_private_data,
+									per_buffer_data);
+
+	return blocknum;
 }
 
 /*
@@ -193,42 +190,12 @@ read_stream_get_block(ReadStream *stream, void *per_buffer_data)
 static inline void
 read_stream_unget_block(ReadStream *stream, BlockNumber blocknum)
 {
-	if (stream->blocknums_next == stream->blocknums_count)
-	{
-		/* Never initialized or entirely consumed.  Re-initialize. */
-		stream->blocknums[0] = blocknum;
-		stream->blocknums_count = 1;
-		stream->blocknums_next = 0;
-	}
-	else
-	{
-		/* Must be the last value return from blocknums array. */
-		Assert(stream->blocknums_next > 0);
-		stream->blocknums_next--;
-		Assert(stream->blocknums[stream->blocknums_next] == blocknum);
-	}
+	/* We shouldn't ever unget more than one block. */
+	Assert(stream->buffered_blocknum == InvalidBlockNumber);
+	Assert(blocknum != InvalidBlockNumber);
+	stream->buffered_blocknum = blocknum;
 }
 
-#ifndef READ_STREAM_DISABLE_FAST_PATH
-static void
-read_stream_fill_blocknums(ReadStream *stream)
-{
-	BlockNumber blocknum;
-	int			i = 0;
-
-	do
-	{
-		blocknum = stream->callback(stream,
-									stream->callback_private_data,
-									NULL);
-		stream->blocknums[i++] = blocknum;
-	} while (i < lengthof(stream->blocknums) &&
-			 blocknum != InvalidBlockNumber);
-	stream->blocknums_count = i;
-	stream->blocknums_next = 0;
-}
-#endif
-
 static void
 read_stream_start_pending_read(ReadStream *stream, bool suppress_advice)
 {
@@ -530,6 +497,7 @@ read_stream_begin_impl(int flags,
 	stream->queue_size = queue_size;
 	stream->callback = callback;
 	stream->callback_private_data = callback_private_data;
+	stream->buffered_blocknum = InvalidBlockNumber;
 
 	/*
 	 * Skip the initial ramp-up phase if the caller says we're going to be
@@ -649,9 +617,7 @@ read_stream_next_buffer(ReadStream *stream, void **per_buffer_data)
 		Assert(buffer != InvalidBuffer);
 
 		/* Choose the next block to pin. */
-		if (unlikely(stream->blocknums_next == stream->blocknums_count))
-			read_stream_fill_blocknums(stream);
-		next_blocknum = stream->blocknums[stream->blocknums_next++];
+		next_blocknum = read_stream_get_block(stream, NULL);
 
 		if (likely(next_blocknum != InvalidBlockNumber))
 		{
@@ -827,9 +793,8 @@ read_stream_reset(ReadStream *stream)
 	/* Stop looking ahead. */
 	stream->distance = 0;
 
-	/* Forget buffered block numbers and fast path state. */
-	stream->blocknums_next = 0;
-	stream->blocknums_count = 0;
+	/* Forget buffered block number and fast path state. */
+	stream->buffered_blocknum = InvalidBlockNumber;
 	stream->fast_path = false;
 
 	/* Unpin anything that wasn't consumed. */