diff --git a/src/main/java/org/qortal/arbitrary/ArbitraryDataBuilder.java b/src/main/java/org/qortal/arbitrary/ArbitraryDataBuilder.java
index 7ef29d03..f8c95596 100644
--- a/src/main/java/org/qortal/arbitrary/ArbitraryDataBuilder.java
+++ b/src/main/java/org/qortal/arbitrary/ArbitraryDataBuilder.java
@@ -154,7 +154,8 @@ public class ArbitraryDataBuilder {
         for (int i=1; i<paths.size(); i++) {
             LOGGER.info(String.format("[%s][%s] Applying layer %d...", this.service, this.name, i));
             Path pathAfter = this.paths.get(i);
-            ArbitraryDataCombiner combiner = new ArbitraryDataCombiner(pathBefore, pathAfter);
+            byte[] signatureBefore = this.transactions.get(i-1).getSignature();
+            ArbitraryDataCombiner combiner = new ArbitraryDataCombiner(pathBefore, pathAfter, signatureBefore);
             combiner.combine();
             combiner.cleanup();
             pathBefore = combiner.getFinalPath();
diff --git a/src/main/java/org/qortal/arbitrary/ArbitraryDataCombiner.java b/src/main/java/org/qortal/arbitrary/ArbitraryDataCombiner.java
index 08409784..3d3fbe9f 100644
--- a/src/main/java/org/qortal/arbitrary/ArbitraryDataCombiner.java
+++ b/src/main/java/org/qortal/arbitrary/ArbitraryDataCombiner.java
@@ -10,6 +10,7 @@ import java.io.IOException;
 import java.nio.file.DirectoryNotEmptyException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.Arrays;
 
 public class ArbitraryDataCombiner {
 
@@ -17,16 +18,19 @@ public class ArbitraryDataCombiner {
 
     private Path pathBefore;
     private Path pathAfter;
+    private byte[] signatureBefore;
     private Path finalPath;
 
-    public ArbitraryDataCombiner(Path pathBefore, Path pathAfter) {
+    public ArbitraryDataCombiner(Path pathBefore, Path pathAfter, byte[] signatureBefore) {
         this.pathBefore = pathBefore;
         this.pathAfter = pathAfter;
+        this.signatureBefore = signatureBefore;
     }
 
     public void combine() throws IOException {
         try {
             this.preExecute();
+            this.validatePreviousSignature();
             this.process();
 
         } finally {
@@ -78,6 +82,24 @@ public class ArbitraryDataCombiner {
 
     }
 
+    private void validatePreviousSignature() throws IOException {
+        if (this.signatureBefore == null) {
+            throw new IllegalStateException("No previous signature passed to the combiner");
+        }
+
+        ArbitraryDataMetadata metadata = new ArbitraryDataMetadata(this.pathAfter);
+        metadata.read();
+        byte[] previousSignature = metadata.getPreviousSignature();
+        if (previousSignature == null) {
+            throw new IllegalStateException("Unable to extract previous signature from patch metadata");
+        }
+
+        // Compare the signatures
+        if (!Arrays.equals(previousSignature, this.signatureBefore)) {
+            throw new IllegalStateException("Previous signatures do not match - transactions out of order?");
+        }
+    }
+
     private void process() throws IOException {
         ArbitraryDataMerge merge = new ArbitraryDataMerge(this.pathBefore, this.pathAfter);
         merge.compute();