diff --git a/pageserver/src/page_cache.rs b/pageserver/src/page_cache.rs
index 1c05ea7e8f..db0a33b55b 100644
--- a/pageserver/src/page_cache.rs
+++ b/pageserver/src/page_cache.rs
@@ -597,17 +597,19 @@ impl PageCache {
         }
     }
 
-    // FIXME: Shouldn't relation size also be tracked with an LSN?
-    // If a replica is lagging behind, it needs to get the size as it was on
-    // the replica's current replay LSN.
-    pub fn relsize_inc(&self, rel: &RelTag, to: Option<u32>) {
+    /// Remember a relation's size in blocks.
+    ///
+    /// If 'to' is larger than the previously remembered size, the remembered size is increased to 'to'.
+    /// But if it's smaller, there is no change.
+    pub fn relsize_inc(&self, rel: &RelTag, to: u32) {
+        // FIXME: Shouldn't relation size also be tracked with an LSN?
+        // If a replica is lagging behind, it needs to get the size as it was on
+        // the replica's current replay LSN.
         let mut shared = self.shared.lock().unwrap();
         let entry = shared.relsize_cache.entry(*rel).or_insert(0);
 
-        if let Some(to) = to {
-            if to >= *entry {
-                *entry = to + 1;
-            }
+        if to >= *entry {
+            *entry = to;
         }
     }
 
diff --git a/pageserver/src/page_service.rs b/pageserver/src/page_service.rs
index f704990f5e..9ff0b2cf46 100644
--- a/pageserver/src/page_service.rs
+++ b/pageserver/src/page_service.rs
@@ -600,7 +600,7 @@ impl Connection {
                         forknum: req.forknum,
                     };
 
-                    pcache.relsize_inc(&tag, None);
+                    pcache.relsize_inc(&tag, 0);
 
                     self.write_message(&BeMessage::ZenithStatusResponse(ZenithStatusResponse {
                         ok: true,
@@ -616,7 +616,7 @@ impl Connection {
                         forknum: req.forknum,
                     };
 
-                    pcache.relsize_inc(&tag, Some(req.blkno));
+                    pcache.relsize_inc(&tag, req.blkno + 1);
 
                     self.write_message(&BeMessage::ZenithStatusResponse(ZenithStatusResponse {
                         ok: true,
diff --git a/pageserver/src/restore_datadir.rs b/pageserver/src/restore_datadir.rs
index 985f5e3905..3b4f303bbc 100644
--- a/pageserver/src/restore_datadir.rs
+++ b/pageserver/src/restore_datadir.rs
@@ -333,7 +333,7 @@ async fn slurp_base_file(
 
         pcache.put_page_image(tag, parsed.lsn, bytes.copy_to_bytes(8192));
 
-        pcache.relsize_inc(&reltag, Some(blknum));
+        pcache.relsize_inc(&reltag, blknum + 1);
         blknum += 1;
     }
 }