diff --git a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala
index 4f27fef..a371710 100644
--- a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala
+++ b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala
@@ -19,11 +19,14 @@ object ProtoEncoder:
  * @param enableNamespaceDeclarations whether to allow namespace declarations in the stream.
  *                                    If true, this will raise the stream version to 2 (Jelly 1.1.0). Otherwise,
  *                                    the stream version will be 1 (Jelly 1.0.0).
+ * @param maybeRowBuffer              optional buffer for storing stream rows that should go into a stream frame.
+ *                                    If provided, the encoder will append the rows to this buffer instead of
+ *                                    returning them, so methods like `addTripleStatement` will return Seq().
  */
 abstract class ProtoEncoder[TNode, -TTriple, -TQuad, -TQuoted](
   final val options: RdfStreamOptions,
   final val enableNamespaceDeclarations: Boolean,
-  final val maybeRowBuffer: Option[mutable.Buffer[RdfStreamRow]] = None,
+  final val maybeRowBuffer: Option[mutable.Buffer[RdfStreamRow]],
 ):
   import ProtoEncoder.*
 
@@ -219,14 +222,15 @@ abstract class ProtoEncoder[TNode, -TTriple, -TQuad, -TQuoted](
     )
 
   private inline def handleHeader(): Unit =
-    if iResponsibleForBufferClear then
-      rowBuffer.clear()
     if !emittedOptions then emitOptions()
     
   private def appendAndReturn(row: RdfStreamRow): Iterable[RdfStreamRow] =
     rowBuffer.append(row)
     // This branch will always be correctly predicted
-    if iResponsibleForBufferClear then rowBuffer.toList
+    if iResponsibleForBufferClear then
+      val list = rowBuffer.toList
+      rowBuffer.clear()
+      list
     else emptyRowBuffer
 
   private def emitOptions(): Unit =
diff --git a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala
index 2e04021..4183637 100644
--- a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala
+++ b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala
@@ -3,7 +3,7 @@ package eu.ostrzyciel.jelly.core
 import eu.ostrzyciel.jelly.core.proto.v1.*
 
 import scala.annotation.switch
-import scala.collection.mutable.ArrayBuffer
+import scala.collection.mutable.ListBuffer
 
 /**
  * Fast implementation of the ProtoTranscoder interface.
@@ -48,7 +48,7 @@ private final class ProtoTranscoderImpl(
   private var inputUsesPrefixes = false
 
   // Current output stream state
-  private val rowBuffer = new ArrayBuffer[RdfStreamRow](128)
+  private val rowBuffer = new ListBuffer[RdfStreamRow]()
   private var changeInTerms = false
   private var emittedOptions = false
 
diff --git a/core/src/test/scala/eu/ostrzyciel/jelly/core/NodeEncoderSpec.scala b/core/src/test/scala/eu/ostrzyciel/jelly/core/NodeEncoderSpec.scala
index ab4d033..a06d103 100644
--- a/core/src/test/scala/eu/ostrzyciel/jelly/core/NodeEncoderSpec.scala
+++ b/core/src/test/scala/eu/ostrzyciel/jelly/core/NodeEncoderSpec.scala
@@ -6,7 +6,7 @@ import org.scalatest.Inspectors
 import org.scalatest.matchers.should.Matchers
 import org.scalatest.wordspec.AnyWordSpec
 
-import scala.collection.mutable.ArrayBuffer
+import scala.collection.mutable.ListBuffer
 import scala.util.Random
 
 class NodeEncoderSpec extends AnyWordSpec, Inspectors, Matchers:
@@ -16,8 +16,8 @@ class NodeEncoderSpec extends AnyWordSpec, Inspectors, Matchers:
     maxDatatypeTableSize = 8,
   )
 
-  private def getEncoder(prefixTableSize: Int = 8): (NodeEncoder[Mrl.Node], ArrayBuffer[RdfStreamRow]) =
-    val buffer = new ArrayBuffer[RdfStreamRow]()
+  private def getEncoder(prefixTableSize: Int = 8): (NodeEncoder[Mrl.Node], ListBuffer[RdfStreamRow]) =
+    val buffer = new ListBuffer[RdfStreamRow]()
     (NodeEncoder[Mrl.Node](smallOptions(prefixTableSize), 16, 16, 16), buffer)
 
   "A NodeEncoder" when {
diff --git a/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoEncoderSpec.scala b/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoEncoderSpec.scala
index f5ae156..a3eceb7 100644
--- a/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoEncoderSpec.scala
+++ b/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoEncoderSpec.scala
@@ -7,6 +7,8 @@ import eu.ostrzyciel.jelly.core.proto.v1.*
 import org.scalatest.matchers.should.Matchers
 import org.scalatest.wordspec.AnyWordSpec
 
+import scala.collection.mutable.ListBuffer
+
 class ProtoEncoderSpec extends AnyWordSpec, Matchers:
   import ProtoTestCases.*
 
@@ -32,6 +34,22 @@ class ProtoEncoderSpec extends AnyWordSpec, Matchers:
       assertEncoded(encoded, Triples2NsDecl.encoded(encoder.options))
     }
 
+    "encode triple statements with ns decls and an external buffer" in {
+      val buffer = ListBuffer[RdfStreamRow]()
+      val encoder = MockProtoEncoder(
+        JellyOptions.smallGeneralized.withPhysicalType(PhysicalStreamType.TRIPLES),
+        enableNamespaceDeclarations = true, Some(buffer)
+      )
+      for triple <- Triples2NsDecl.mrl do
+        val result = triple match
+          case t: Triple => encoder.addTripleStatement(t)
+          case ns: NamespaceDecl => encoder.declareNamespace(ns.name, ns.iri)
+        // external buffer – nothing should be returned directly
+        result.size should be (0)
+
+      assertEncoded(buffer.toSeq, Triples2NsDecl.encoded(encoder.options))
+    }
+
     "encode quad statements" in {
       val encoder = MockProtoEncoder(
         JellyOptions.smallGeneralized.withPhysicalType(PhysicalStreamType.QUADS)
@@ -40,6 +58,20 @@ class ProtoEncoderSpec extends AnyWordSpec, Matchers:
       assertEncoded(encoded, Quads1.encoded(encoder.options.withVersion(Constants.protoVersionNoNsDecl)))
     }
 
+    "encode quad statements with an external buffer" in {
+      val buffer = ListBuffer[RdfStreamRow]()
+      val encoder = MockProtoEncoder(
+        JellyOptions.smallGeneralized.withPhysicalType(PhysicalStreamType.QUADS),
+        false, Some(buffer)
+      )
+      for quad <- Quads1.mrl do
+        val result = encoder.addQuadStatement(quad)
+        // external buffer – nothing should be returned directly
+        result.size should be (0)
+
+      assertEncoded(buffer.toSeq, Quads1.encoded(encoder.options.withVersion(Constants.protoVersionNoNsDecl)))
+    }
+
     "encode quad statements (repeated default graph)" in {
       val encoder = MockProtoEncoder(
         JellyOptions.smallGeneralized.withPhysicalType(PhysicalStreamType.QUADS)
@@ -60,6 +92,24 @@ class ProtoEncoderSpec extends AnyWordSpec, Matchers:
       assertEncoded(encoded, Graphs1.encoded(encoder.options.withVersion(Constants.protoVersionNoNsDecl)))
     }
 
+    "encode graphs with an external buffer" in {
+      val buffer = ListBuffer[RdfStreamRow]()
+      val encoder = MockProtoEncoder(
+        JellyOptions.smallGeneralized.withPhysicalType(PhysicalStreamType.GRAPHS),
+        false, Some(buffer)
+      )
+      for (graphName, triples) <- Graphs1.mrl do
+        val start = encoder.startGraph(graphName)
+        start.size should be (0)
+        for triple <- triples do
+          val result = encoder.addTripleStatement(triple)
+          result.size should be (0)
+        val end = encoder.endGraph()
+        end.size should be (0)
+
+      assertEncoded(buffer.toSeq, Graphs1.encoded(encoder.options.withVersion(Constants.protoVersionNoNsDecl)))
+    }
+
     "not allow to end a graph before starting one" in {
       val encoder = MockProtoEncoder(
         JellyOptions.smallGeneralized.withPhysicalType(PhysicalStreamType.QUADS)
diff --git a/jena/src/main/scala/eu/ostrzyciel/jelly/convert/jena/riot/JellyWriter.scala b/jena/src/main/scala/eu/ostrzyciel/jelly/convert/jena/riot/JellyWriter.scala
index cc84af1..58c55bf 100644
--- a/jena/src/main/scala/eu/ostrzyciel/jelly/convert/jena/riot/JellyWriter.scala
+++ b/jena/src/main/scala/eu/ostrzyciel/jelly/convert/jena/riot/JellyWriter.scala
@@ -10,7 +10,7 @@ import org.apache.jena.sparql.core.{DatasetGraph, Quad}
 import org.apache.jena.sparql.util.Context
 
 import java.io.{OutputStream, Writer}
-import scala.collection.mutable.{ArrayBuffer, ListBuffer}
+import scala.collection.mutable.ListBuffer
 import scala.jdk.CollectionConverters.*
 
 
diff --git a/rdf4j/src/main/scala/eu/ostrzyciel/jelly/convert/rdf4j/rio/JellyWriter.scala b/rdf4j/src/main/scala/eu/ostrzyciel/jelly/convert/rdf4j/rio/JellyWriter.scala
index 914c8f7..62ae853 100644
--- a/rdf4j/src/main/scala/eu/ostrzyciel/jelly/convert/rdf4j/rio/JellyWriter.scala
+++ b/rdf4j/src/main/scala/eu/ostrzyciel/jelly/convert/rdf4j/rio/JellyWriter.scala
@@ -8,7 +8,7 @@ import org.eclipse.rdf4j.rio.helpers.AbstractRDFWriter
 
 import java.io.OutputStream
 import java.util
-import scala.collection.mutable.{ArrayBuffer, ListBuffer}
+import scala.collection.mutable.ListBuffer
 
 /**
  * RDF4J Rio writer for Jelly RDF format.