diff --git a/runtime/src/main/java/org/capnproto/BuilderArena.java b/runtime/src/main/java/org/capnproto/BuilderArena.java
index b9da6c3..1fab160 100644
--- a/runtime/src/main/java/org/capnproto/BuilderArena.java
+++ b/runtime/src/main/java/org/capnproto/BuilderArena.java
@@ -27,7 +27,6 @@ public final class BuilderArena implements Arena {
         this.allocationStrategy = allocationStrategy;
         SegmentBuilder segment0 = new SegmentBuilder(
             ByteBuffer.allocate(firstSegmentSizeWords * Constants.BYTES_PER_WORD), this);
-        segment0.buffer.mark();
         segment0.buffer.order(ByteOrder.LITTLE_ENDIAN);
         this.segments.add(segment0);
     }
@@ -78,7 +77,6 @@ public final class BuilderArena implements Arena {
 
         // --------
 
-        newSegment.buffer.mark();
         newSegment.buffer.order(ByteOrder.LITTLE_ENDIAN);
         newSegment.id = len;
         this.segments.add(newSegment);
diff --git a/runtime/src/main/java/org/capnproto/SegmentBuilder.java b/runtime/src/main/java/org/capnproto/SegmentBuilder.java
index 5448ca3..86bf6b3 100644
--- a/runtime/src/main/java/org/capnproto/SegmentBuilder.java
+++ b/runtime/src/main/java/org/capnproto/SegmentBuilder.java
@@ -15,7 +15,7 @@ public final class SegmentBuilder extends SegmentReader {
 
     // the total number of words the buffer can hold
     private final int capacity() {
-        this.buffer.reset();
+        this.buffer.rewind();
         return this.buffer.remaining() / 8;
     }
 
diff --git a/runtime/src/test/scala/org/capnproto/LayoutTest.scala b/runtime/src/test/scala/org/capnproto/LayoutTest.scala
index c7ac0c2..85a466a 100644
--- a/runtime/src/test/scala/org/capnproto/LayoutTest.scala
+++ b/runtime/src/test/scala/org/capnproto/LayoutTest.scala
@@ -90,7 +90,6 @@ class LayoutSuite extends FunSuite {
   test("StructRoundTrip_OneSegment") {
     val buffer = java.nio.ByteBuffer.allocate(1024 * 8);
     buffer.order(java.nio.ByteOrder.LITTLE_ENDIAN);
-    buffer.mark();
 
     val pointerBuilder = PointerBuilder.getRoot(
       new SegmentBuilder(buffer, new BuilderArena(BuilderArena.SUGGESTED_FIRST_SEGMENT_WORDS,