diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
index cfe3635..3bd8b25 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
@@ -20,7 +20,8 @@
  */
 public record ByteString(byte[] bytes) {
 
-  private static final Decoder<ByteString> DECODER = Decoder.ofByteArray().map(ByteString::new);
+  private static final Decoder<ByteString> DECODER =
+      Decoder.ofByteArray().map(ByteString::new, ByteString::bytes);
 
   /**
    * Returns a decoder for a {@code byte[]} that wraps the result in {@link ByteString}.
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java
index 261e2be..829664e 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java
@@ -17,7 +17,8 @@
 
   private static final int SIZE = 32;
 
-  private static final Decoder<Checksum> DECODER = ByteString.decoder().map(Checksum::new);
+  private static final Decoder<Checksum> DECODER =
+      ByteString.decoder().map(Checksum::new, Checksum::byteString);
 
   public Checksum {
     if (byteString.size() == 0) {
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java
index 57c8fc5..08e0b8c 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java
@@ -25,7 +25,7 @@
   private static final Decoder<DeltaFallback> DECODER =
       Decoder.ofStructure(
           DeltaFallback.class,
-          Decoder.ofByte().map(ObjectType::valueOf),
+          Decoder.ofByte().map(ObjectType::valueOf, ObjectType::byteValue),
           Checksum.decoder(),
           Decoder.ofLong(),
           Decoder.ofLong());
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java
index 8c6fd19..2be0426 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java
@@ -5,6 +5,7 @@
 package eu.mulk.jgvariant.ostree;
 
 import eu.mulk.jgvariant.core.Decoder;
+import java.io.ByteArrayOutputStream;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.util.ArrayList;
@@ -38,7 +39,9 @@
 
     private static final Decoder<DeltaObject> DECODER =
         Decoder.ofStructure(
-            DeltaObject.class, Decoder.ofByte().map(ObjectType::valueOf), Checksum.decoder());
+            DeltaObject.class,
+            Decoder.ofByte().map(ObjectType::valueOf, ObjectType::byteValue),
+            Checksum.decoder());
 
     /**
      * Acquires a {@link Decoder} for the enclosing type.
@@ -57,7 +60,19 @@
           Checksum.decoder(),
           Decoder.ofLong(),
           Decoder.ofLong(),
-          Decoder.ofByteArray().map(DeltaMetaEntry::parseObjectList));
+          Decoder.ofByteArray()
+              .map(DeltaMetaEntry::parseObjectList, DeltaMetaEntry::serializeObjectList));
+
+  private static byte[] serializeObjectList(List<DeltaObject> deltaObjects) {
+    var output = new ByteArrayOutputStream();
+
+    for (var deltaObject : deltaObjects) {
+      output.write(deltaObject.objectType.byteValue());
+      output.writeBytes(deltaObject.checksum.byteString().bytes());
+    }
+
+    return output.toByteArray();
+  }
 
   private static List<DeltaObject> parseObjectList(byte[] bytes) {
     var byteBuffer = ByteBuffer.wrap(bytes);
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaOperation.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaOperation.java
index 6edf217..d753a48 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaOperation.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaOperation.java
@@ -4,6 +4,7 @@
 
 package eu.mulk.jgvariant.ostree;
 
+import java.io.ByteArrayOutputStream;
 import java.nio.ByteBuffer;
 
 /** An operation in a static delta. */
@@ -67,6 +68,42 @@
     };
   }
 
+  default void writeTo(ByteArrayOutputStream output) {
+    if (this instanceof OpenSpliceAndCloseMeta openSpliceAndCloseMeta) {
+      output.write(DeltaOperationType.OPEN_SPLICE_AND_CLOSE.byteValue());
+      writeVarint64(output, openSpliceAndCloseMeta.offset);
+      writeVarint64(output, openSpliceAndCloseMeta.size);
+    } else if (this instanceof OpenSpliceAndCloseReal openSpliceAndCloseReal) {
+      output.write(DeltaOperationType.OPEN_SPLICE_AND_CLOSE.byteValue());
+      writeVarint64(output, openSpliceAndCloseReal.modeOffset);
+      writeVarint64(output, openSpliceAndCloseReal.xattrOffset);
+      writeVarint64(output, openSpliceAndCloseReal.size);
+      writeVarint64(output, openSpliceAndCloseReal.offset);
+    } else if (this instanceof Open open) {
+      output.write(DeltaOperationType.OPEN.byteValue());
+      writeVarint64(output, open.modeOffset);
+      writeVarint64(output, open.xattrOffset);
+      writeVarint64(output, open.size);
+    } else if (this instanceof Write write) {
+      output.write(DeltaOperationType.WRITE.byteValue());
+      writeVarint64(output, write.size);
+      writeVarint64(output, write.offset);
+    } else if (this instanceof SetReadSource setReadSource) {
+      output.write(DeltaOperationType.SET_READ_SOURCE.byteValue());
+      writeVarint64(output, setReadSource.offset);
+    } else if (this instanceof UnsetReadSource) {
+      output.write(DeltaOperationType.UNSET_READ_SOURCE.byteValue());
+    } else if (this instanceof Close) {
+      output.write(DeltaOperationType.CLOSE.byteValue());
+    } else if (this instanceof BsPatch bsPatch) {
+      output.write(DeltaOperationType.BSPATCH.byteValue());
+      writeVarint64(output, bsPatch.offset);
+      writeVarint64(output, bsPatch.size);
+    } else {
+      throw new IllegalStateException("unrecognized delta operation: %s".formatted(this));
+    }
+  }
+
   /**
    * Reads a Protobuf varint from a byte buffer.
    *
@@ -86,4 +123,23 @@
 
     return acc;
   }
+
+  /**
+   * Writes a Protobuf varint to an output stream.
+   *
+   * @see #readVarint64
+   */
+  private static void writeVarint64(ByteArrayOutputStream output, long value) {
+    while (value != 0) {
+      byte b = (byte) (value & 0x7F);
+      value >>= 7;
+      if (value != 0) {
+        b |= (byte) 0x80;
+      }
+      output.write(b);
+      if (value == 0) {
+        break;
+      }
+    }
+  }
 }
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java
index f89d414..31c192d 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java
@@ -8,12 +8,14 @@
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
+import java.nio.channels.Channels;
 import java.util.ArrayList;
 import java.util.List;
+import org.tukaani.xz.LZMA2Options;
 import org.tukaani.xz.XZInputStream;
+import org.tukaani.xz.XZOutputStream;
 
 /**
  * A payload file from a static delta.
@@ -36,7 +38,7 @@
     ByteString rawDataSource,
     List<DeltaOperation> operations) {
 
-  private static ByteBuffer preparse(ByteBuffer byteBuffer) {
+  private static ByteBuffer decompress(ByteBuffer byteBuffer) {
     byte compressionByte = byteBuffer.get(0);
     var dataSlice = byteBuffer.slice(1, byteBuffer.limit() - 1);
     return switch (compressionByte) {
@@ -53,7 +55,7 @@
           yield ByteBuffer.wrap(decompressedOutputStream.toByteArray());
         } catch (IOException e) {
           // impossible
-          throw new UncheckedIOException(e);
+          throw new IllegalStateException(e);
         }
       }
       default -> throw new IllegalArgumentException(
@@ -61,10 +63,42 @@
     };
   }
 
+  private static ByteBuffer compress(ByteBuffer dataSlice) {
+    var dataBytes = new byte[dataSlice.limit()];
+    dataSlice.get(dataBytes);
+    var compressedOutputStream = new ByteArrayOutputStream();
+
+    byte compressionByte = 'x';
+    compressedOutputStream.write(compressionByte);
+
+    try (var compressingOutputStream =
+            new XZOutputStream(compressedOutputStream, new LZMA2Options());
+        var compressingChannel = Channels.newChannel(compressingOutputStream)) {
+      compressingChannel.write(dataSlice);
+      compressingOutputStream.write(dataBytes);
+    } catch (IOException e) {
+      // impossible
+      throw new IllegalStateException(e);
+    }
+
+    var compressedBytes = compressedOutputStream.toByteArray();
+    return ByteBuffer.wrap(compressedBytes);
+  }
+
+  private static byte[] serializeDeltaOperationList(List<DeltaOperation> deltaOperations) {
+    var output = new ByteArrayOutputStream();
+
+    for (var currentOperation : deltaOperations) {
+      currentOperation.writeTo(output);
+    }
+
+    return output.toByteArray();
+  }
+
   private static List<DeltaOperation> parseDeltaOperationList(
-      ByteString byteString, List<ObjectType> objectTypes) {
+      byte[] bytes, List<ObjectType> objectTypes) {
     List<DeltaOperation> deltaOperations = new ArrayList<>();
-    var byteBuffer = ByteBuffer.wrap(byteString.bytes());
+    var byteBuffer = ByteBuffer.wrap(bytes);
     int objectIndex = 0;
 
     while (byteBuffer.hasRemaining()) {
@@ -119,8 +153,10 @@
             Decoder.ofArray(FileMode.decoder()),
             Decoder.ofArray(Decoder.ofArray(Xattr.decoder())),
             ByteString.decoder(),
-            ByteString.decoder()
-                .map(byteString -> parseDeltaOperationList(byteString, objectTypes)))
-        .contramap(DeltaPartPayload::preparse);
+            Decoder.ofByteArray()
+                .map(
+                    bytes -> parseDeltaOperationList(bytes, objectTypes),
+                    deltaOperations -> serializeDeltaOperationList(deltaOperations)))
+        .contramap(DeltaPartPayload::decompress, DeltaPartPayload::compress);
   }
 }
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
index 50da203..9513fa0 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
@@ -5,10 +5,16 @@
 package eu.mulk.jgvariant.ostree;
 
 import eu.mulk.jgvariant.core.Decoder;
+import eu.mulk.jgvariant.core.Signature;
+import eu.mulk.jgvariant.core.Variant;
+import java.io.ByteArrayOutputStream;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
+import java.text.ParseException;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 /**
  * A static delta.
@@ -67,10 +73,34 @@
               Checksum.decoder(),
               Checksum.decoder(),
               Commit.decoder(),
-              Decoder.ofByteArray().map(DeltaSuperblock::parseDeltaNameList),
+              Decoder.ofByteArray()
+                  .map(
+                      DeltaSuperblock::parseDeltaNameList, DeltaSuperblock::serializeDeltaNameList),
               Decoder.ofArray(DeltaMetaEntry.decoder()).withByteOrder(ByteOrder.LITTLE_ENDIAN),
               Decoder.ofArray(DeltaFallback.decoder()).withByteOrder(ByteOrder.LITTLE_ENDIAN))
-          .map(DeltaSuperblock::byteSwappedIfBigEndian);
+          .map(DeltaSuperblock::byteSwappedIfBigEndian, DeltaSuperblock::withSpecifiedByteOrder);
+
+  private DeltaSuperblock withSpecifiedByteOrder() {
+    Map<String, Variant> extendedMetadataMap = new HashMap<>(metadata().fields());
+
+    try {
+      extendedMetadataMap.putIfAbsent(
+          "ostree.endianness", new Variant(Signature.parse("y"), (byte) 'l'));
+    } catch (ParseException e) {
+      // impossible
+      throw new IllegalStateException(e);
+    }
+
+    return new DeltaSuperblock(
+        new Metadata(extendedMetadataMap),
+        timestamp,
+        fromChecksum,
+        toChecksum,
+        commit,
+        dependencies,
+        entries,
+        fallbacks);
+  }
 
   private DeltaSuperblock byteSwappedIfBigEndian() {
     // Fix up the endianness of the 'entries' and 'fallbacks' fields, which have
@@ -97,6 +127,17 @@
         fallbacks.stream().map(DeltaFallback::byteSwapped).toList());
   }
 
+  private static byte[] serializeDeltaNameList(List<DeltaName> deltaNames) {
+    var output = new ByteArrayOutputStream();
+
+    for (var deltaName : deltaNames) {
+      output.writeBytes(deltaName.fromChecksum().byteString().bytes());
+      output.writeBytes(deltaName.toChecksum().byteString().bytes());
+    }
+
+    return output.toByteArray();
+  }
+
   private static List<DeltaName> parseDeltaNameList(byte[] bytes) {
     var byteBuffer = ByteBuffer.wrap(bytes);
     List<DeltaName> deltaNames = new ArrayList<>();
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
index 62f0331..f485be1 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
@@ -20,7 +20,8 @@
 public record Metadata(Map<String, Variant> fields) {
 
   private static final Decoder<Metadata> DECODER =
-      Decoder.ofDictionary(Decoder.ofString(UTF_8), Decoder.ofVariant()).map(Metadata::new);
+      Decoder.ofDictionary(Decoder.ofString(UTF_8), Decoder.ofVariant())
+          .map(Metadata::new, Metadata::fields);
 
   /**
    * Acquires a {@link Decoder} for the enclosing type.
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java
index 827d5e4..1e1e58e 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java
@@ -31,11 +31,18 @@
       Decoder.ofStructure(
           SignedDelta.class,
           Decoder.ofLong().withByteOrder(ByteOrder.BIG_ENDIAN),
-          ByteString.decoder().map(SignedDelta::decodeSuperblock),
+          Decoder.ofByteArray().map(SignedDelta::decodeSuperblock, SignedDelta::encodeSuperblock),
           Decoder.ofDictionary(Decoder.ofString(US_ASCII), Decoder.ofVariant()));
 
-  private static DeltaSuperblock decodeSuperblock(ByteString byteString) {
-    return DeltaSuperblock.decoder().decode(ByteBuffer.wrap(byteString.bytes()));
+  private static DeltaSuperblock decodeSuperblock(byte[] bytes) {
+    return DeltaSuperblock.decoder().decode(ByteBuffer.wrap(bytes));
+  }
+
+  private static byte[] encodeSuperblock(DeltaSuperblock deltaSuperblock) {
+    var byteBuffer = DeltaSuperblock.decoder().encode(deltaSuperblock);
+    byte[] bytes = new byte[byteBuffer.remaining()];
+    byteBuffer.get(bytes);
+    return bytes;
   }
 
   /**
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java
index 3c88759..5834c91 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java
@@ -22,7 +22,8 @@
 public record SummarySignature(Map<String, Variant> signatures) {
 
   private static final Decoder<SummarySignature> DECODER =
-      Decoder.ofDictionary(Decoder.ofString(UTF_8), Decoder.ofVariant()).map(SummarySignature::new);
+      Decoder.ofDictionary(Decoder.ofString(UTF_8), Decoder.ofVariant())
+          .map(SummarySignature::new, SummarySignature::signatures);
 
   /**
    * Acquires a {@link Decoder} for the enclosing type.