diff --git a/libs/pageserver_api/src/keyspace.rs b/libs/pageserver_api/src/keyspace.rs
index 16651c322e..80183506d8 100644
--- a/libs/pageserver_api/src/keyspace.rs
+++ b/libs/pageserver_api/src/keyspace.rs
@@ -124,6 +124,9 @@ impl KeySpaceAccum {
                 if range.start == accum.end {
                     accum.end = range.end;
                 } else {
+                    // TODO: to efficiently support small sharding stripe sizes, we should avoid starting
+                    // a new range here if the skipped region was all keys that don't belong on this shard.
+                    // (https://github.com/neondatabase/neon/issues/6247)
                     assert!(range.start > accum.end);
                     self.ranges.push(accum.clone());
                     *accum = range;
diff --git a/libs/pageserver_api/src/shard.rs b/libs/pageserver_api/src/shard.rs
index 3e4936eec4..a186d93bce 100644
--- a/libs/pageserver_api/src/shard.rs
+++ b/libs/pageserver_api/src/shard.rs
@@ -422,6 +422,21 @@ impl ShardIdentity {
         }
     }
 
+    /// Return true if the key should be discarded if found in this shard's
+    /// data store, e.g. during compaction after a split
+    pub fn is_key_disposable(&self, key: &Key) -> bool {
+        if key_is_shard0(key) {
+            // Q: Why can't we dispose of shard0 content if we're not shard 0?
+            // A: because the WAL ingestion logic currently ingests some shard 0
+            //    content on all shards, even though it's only read on shard 0.  If we
+            //    dropped it, then subsequent WAL ingest to these keys would encounter
+            //    an error.
+            false
+        } else {
+            !self.is_key_local(key)
+        }
+    }
+
     pub fn shard_slug(&self) -> String {
         if self.count > ShardCount(0) {
             format!("-{:02x}{:02x}", self.number.0, self.count.0)
diff --git a/pageserver/src/tenant/timeline.rs b/pageserver/src/tenant/timeline.rs
index 15a5ca1727..e8340a74b2 100644
--- a/pageserver/src/tenant/timeline.rs
+++ b/pageserver/src/tenant/timeline.rs
@@ -496,6 +496,11 @@ impl Timeline {
             return Err(PageReconstructError::Other(anyhow::anyhow!("Invalid LSN")));
         }
 
+        // This check is debug-only because of the cost of hashing, and because it's a double-check: we
+        // already checked the key against the shard_identity when looking up the Timeline from
+        // page_service.
+        debug_assert!(!self.shard_identity.is_key_disposable(&key));
+
         // XXX: structured stats collection for layer eviction here.
         trace!(
             "get page request for {}@{} from task kind {:?}",
@@ -2224,13 +2229,13 @@ impl Timeline {
                     return Err(layer_traversal_error(
                         if cfg!(test) {
                             format!(
-                                "could not find data for key {} at LSN {}, for request at LSN {}\n{}",
-                                key, cont_lsn, request_lsn, std::backtrace::Backtrace::force_capture(),
+                                "could not find data for key {} (shard {:?}) at LSN {}, for request at LSN {}\n{}",
+                                key, self.shard_identity.get_shard_number(&key), cont_lsn, request_lsn, std::backtrace::Backtrace::force_capture(),
                             )
                         } else {
                             format!(
-                                "could not find data for key {} at LSN {}, for request at LSN {}",
-                                key, cont_lsn, request_lsn
+                                "could not find data for key {} (shard {:?}) at LSN {}, for request at LSN {}",
+                                key, self.shard_identity.get_shard_number(&key), cont_lsn, request_lsn
                             )
                         },
                         traversal_path,
@@ -3054,6 +3059,15 @@ impl Timeline {
                 for range in &partition.ranges {
                     let mut key = range.start;
                     while key < range.end {
+                        if self.shard_identity.is_key_disposable(&key) {
+                            debug!(
+                                "Dropping key {} during compaction (it belongs on shard {:?})",
+                                key,
+                                self.shard_identity.get_shard_number(&key)
+                            );
+                            key = key.next();
+                            continue;
+                        }
                         let img = match self.get(key, lsn, ctx).await {
                             Ok(img) => img,
                             Err(err) => {
@@ -3080,6 +3094,7 @@ impl Timeline {
                                 }
                             }
                         };
+
                         image_layer_writer.put_image(key, &img).await?;
                         key = key.next();
                     }
@@ -3650,7 +3665,15 @@ impl Timeline {
                 )))
             });
 
-            writer.as_mut().unwrap().put_value(key, lsn, value).await?;
+            if !self.shard_identity.is_key_disposable(&key) {
+                writer.as_mut().unwrap().put_value(key, lsn, value).await?;
+            } else {
+                debug!(
+                    "Dropping key {} during compaction (it belongs on shard {:?})",
+                    key,
+                    self.shard_identity.get_shard_number(&key)
+                );
+            }
 
             if !new_layers.is_empty() {
                 fail_point!("after-timeline-compacted-first-L1");