diff --git a/crates/runner-shared/src/artifacts/memtrack/mod.rs b/crates/runner-shared/src/artifacts/memtrack/mod.rs
index 962095077..f799ada9e 100644
--- a/crates/runner-shared/src/artifacts/memtrack/mod.rs
+++ b/crates/runner-shared/src/artifacts/memtrack/mod.rs
@@ -26,13 +26,19 @@ impl super::ArtifactExt for MemtrackArtifact {
 impl MemtrackArtifact {
     /// The msgpack decoder reads a few bytes per call, so the decompressed
     /// stream is buffered rather than read straight from the zstd decoder.
+    /// The buffer is sized well above a stack record's 8 KiB byte field.
     #[allow(clippy::type_complexity)]
     pub fn decode_streamed<R: std::io::Read>(
         reader: R,
     ) -> anyhow::Result<MemtrackEventStream<BufReader<zstd::Decoder<'static, BufReader<R>>>>> {
+        const BUFFER_SIZE: usize = 1024 * 1024;
+
         let decoder = zstd::Decoder::new(reader)?;
         Ok(MemtrackEventStream {
-            deserializer: rmp_serde::Deserializer::new(BufReader::new(decoder)),
+            deserializer: rmp_serde::Deserializer::new(BufReader::with_capacity(
+                BUFFER_SIZE,
+                decoder,
+            )),
         })
     }