diff --git a/CHANGELOG.next.asciidoc b/CHANGELOG.next.asciidoc
index 3f999f677822..25a6b617a637 100644
--- a/CHANGELOG.next.asciidoc
+++ b/CHANGELOG.next.asciidoc
@@ -71,9 +71,8 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Upgraded apache arrow library used in x-pack/libbeat/reader/parquet from v11 to v12.0.1 in order to fix cross-compilation issues {pull}35640[35640]
 - Fix panic when MaxRetryInterval is specified, but RetryInterval is not {pull}35820[35820]
 - Do not print context cancelled error message when running under agent {pull}36006[36006]
-
-
 - Fix recovering from invalid output configuration when running under Elastic-Agent {pull}36016[36016]
+- Improve StreamBuf append to improve performance when reading long lines from files. {pull}35928[35928]
 
 *Auditbeat*
 
diff --git a/libbeat/common/streambuf/streambuf.go b/libbeat/common/streambuf/streambuf.go
index f28c21577920..48bbabae0d5f 100644
--- a/libbeat/common/streambuf/streambuf.go
+++ b/libbeat/common/streambuf/streambuf.go
@@ -155,7 +155,9 @@ func (b *Buffer) doAppend(data []byte, retainable bool, newCap int) error {
 				b.data = tmp
 			}
 		}
-		b.data = append(b.data, data...)
+		tBuf := bytes.NewBuffer(b.data)
+		tBuf.Write(data)
+		b.data = tBuf.Bytes()
 	}
 	b.available += len(data)