diff --git a/libs/pageserver_api/src/value.rs b/libs/pageserver_api/src/value.rs
index 883d903ff3..e9000939c3 100644
--- a/libs/pageserver_api/src/value.rs
+++ b/libs/pageserver_api/src/value.rs
@@ -36,6 +36,24 @@ impl Value {
             Value::WalRecord(rec) => rec.will_init(),
         }
     }
+
+    #[inline(always)]
+    pub fn estimated_size(&self) -> usize {
+        match self {
+            Value::Image(image) => image.len(),
+            Value::WalRecord(NeonWalRecord::AuxFile {
+                content: Some(content),
+                ..
+            }) => content.len(),
+            Value::WalRecord(NeonWalRecord::Postgres { rec, .. }) => rec.len(),
+            Value::WalRecord(NeonWalRecord::ClogSetAborted { xids }) => xids.len() * 4,
+            Value::WalRecord(NeonWalRecord::ClogSetCommitted { xids, .. }) => xids.len() * 4,
+            Value::WalRecord(NeonWalRecord::MultixactMembersCreate { members, .. }) => {
+                members.len() * 8
+            }
+            _ => 8192, /* use image size as the estimation */
+        }
+    }
 }
 
 #[derive(Debug, PartialEq)]
diff --git a/pageserver/src/tenant/timeline/compaction.rs b/pageserver/src/tenant/timeline/compaction.rs
index e7d39db70d..37c1a8f60c 100644
--- a/pageserver/src/tenant/timeline/compaction.rs
+++ b/pageserver/src/tenant/timeline/compaction.rs
@@ -3435,6 +3435,7 @@ impl Timeline {
 
         // Step 2: Produce images+deltas.
         let mut accumulated_values = Vec::new();
+        let mut accumulated_values_estimated_size = 0;
         let mut last_key: Option<Key> = None;
 
         // Only create image layers when there is no ancestor branches. TODO: create covering image layer
@@ -3611,12 +3612,16 @@ impl Timeline {
                 if last_key.is_none() {
                     last_key = Some(key);
                 }
+                accumulated_values_estimated_size += val.estimated_size();
                 accumulated_values.push((key, lsn, val));
 
-                if accumulated_values.len() >= 65536 {
-                    // Assume all of them are images, that would be 512MB of data in memory for a single key.
+                // Accumulated values should never exceed 512MB.
+                if accumulated_values_estimated_size >= 1024 * 1024 * 512 {
                     return Err(CompactionError::Other(anyhow!(
-                        "too many values for a single key, giving up gc-compaction"
+                        "too many values for a single key: {} for key {}, {} items",
+                        accumulated_values_estimated_size,
+                        key,
+                        accumulated_values.len()
                     )));
                 }
             } else {
@@ -3651,6 +3656,7 @@ impl Timeline {
                     .map_err(CompactionError::Other)?;
                 accumulated_values.clear();
                 *last_key = key;
+                accumulated_values_estimated_size = val.estimated_size();
                 accumulated_values.push((key, lsn, val));
             }
         }