diff --git a/pgxn/neon/communicator/src/neon_request.rs b/pgxn/neon/communicator/src/neon_request.rs
index 4b5be0b34c..95fab449f6 100644
--- a/pgxn/neon/communicator/src/neon_request.rs
+++ b/pgxn/neon/communicator/src/neon_request.rs
@@ -190,8 +190,7 @@ pub struct CRelExtendRequest {
     pub lsn: CLsn,
 
     // These fields define page contents. Must point into a buffer in shared memory!
-    pub src_ptr: usize,
-    pub src_size: u32,
+    pub src: ShmemBuf,
 }
 
 #[repr(C)]
diff --git a/pgxn/neon/communicator/src/worker_process/main_loop.rs b/pgxn/neon/communicator/src/worker_process/main_loop.rs
index 24be5f4987..42483e67ea 100644
--- a/pgxn/neon/communicator/src/worker_process/main_loop.rs
+++ b/pgxn/neon/communicator/src/worker_process/main_loop.rs
@@ -231,8 +231,28 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
     }
 
     fn request_lsns(&self, not_modified_since_lsn: Lsn) -> page_api::ReadLsn {
+        let mut request_lsn = get_request_lsn();
+
+	// Is it possible that the last-written LSN is ahead of last flush
+	// LSN? Generally not, we shouldn't evict a page from the buffer cache
+	// before all its modifications have been safely flushed. That's the
+	// "WAL before data" rule. However, such case does exist at index
+	// building, _bt_blwritepage logs the full page without flushing WAL
+	// before smgrextend (files are fsynced before build ends).
+        //
+        // FIXME: I'm seeing some other cases of this too in the regression tests.
+        // Maybe it's OK? Would be nice to dig a little deeper.
+        // See the old logic in neon_get_request_lsns() C function
+        if not_modified_since_lsn > request_lsn {
+            tracing::info!(
+                "not_modified_since_lsn {} is ahead of last flushed LSN {}",
+                not_modified_since_lsn, request_lsn
+            );
+            request_lsn = not_modified_since_lsn;
+        }
+
         page_api::ReadLsn {
-            request_lsn: get_request_lsn(),
+            request_lsn,
             not_modified_since_lsn: Some(not_modified_since_lsn),
         }
     }
@@ -371,7 +391,13 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
             NeonIORequest::RelExtend(req) => {
                 self.request_rel_extend_counter.inc();
 
-                // TODO: need to grab an io-in-progress lock for this? I guess not
+                let rel = req.reltag();
+                let _in_progress_guard = self
+                    .in_progress_table
+                    .lock(RequestInProgressKey::Block(rel, req.block_number));
+                self.cache
+                    .remember_page(&rel, req.block_number, req.src, Lsn(req.lsn), true)
+                    .await;
                 self.cache
                     .remember_rel_size(&req.reltag(), req.block_number + 1);
                 NeonIOResult::WriteOK
@@ -382,6 +408,8 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
                     .inc_by(req.nblocks as u64);
 
                 // TODO: need to grab an io-in-progress lock for this? I guess not
+                // TODO: I think we should put the empty pages to the cache, or at least
+                // update the last-written LSN.
                 self.cache
                     .remember_rel_size(&req.reltag(), req.block_number + req.nblocks);
                 NeonIOResult::WriteOK
@@ -461,12 +489,13 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
 
         // TODO: Use batched protocol
         for (blkno, _lsn, dest, _guard) in cache_misses.iter() {
+            let read_lsn = self.request_lsns(not_modified_since);
             match self
                 .client
                 .get_page(page_api::GetPageRequest {
                     request_id: self.next_request_id.fetch_add(1, Ordering::Relaxed),
                     request_class: page_api::GetPageClass::Normal,
-                    read_lsn: self.request_lsns(not_modified_since),
+                    read_lsn: read_lsn,
                     rel,
                     block_numbers: vec![*blkno],
                 })
@@ -491,7 +520,7 @@ impl<'t> CommunicatorWorkerProcessStruct<'t> {
 
                     // Also store it in the LFC while we have it
                     self.cache
-                        .remember_page(&rel, *blkno, page_image, not_modified_since, false)
+                        .remember_page(&rel, *blkno, page_image, read_lsn.not_modified_since_lsn.unwrap(), false)
                         .await;
                 }
                 Err(err) => {
diff --git a/pgxn/neon/communicator_new.c b/pgxn/neon/communicator_new.c
index fa9dac7705..5f8d8788e2 100644
--- a/pgxn/neon/communicator_new.c
+++ b/pgxn/neon/communicator_new.c
@@ -866,8 +866,7 @@ communicator_new_rel_extend(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber
 			.fork_number = forkNum,
 			.block_number = blockno,
 			.lsn = lsn,
-			.src_ptr = (uintptr_t) src,
-			.src_size = BLCKSZ,
+			.src.ptr = src,
 		}
 	};
 	NeonIOResult result;