diff --git a/core/src/main/java/org/bitcoinj/core/GetUTXOsMessage.java b/core/src/main/java/org/bitcoinj/core/GetUTXOsMessage.java
index 0b722fb1..a887a492 100644
--- a/core/src/main/java/org/bitcoinj/core/GetUTXOsMessage.java
+++ b/core/src/main/java/org/bitcoinj/core/GetUTXOsMessage.java
@@ -22,8 +22,17 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.util.List;
 
+/**
+ * This command is supported only by <a href="http://github.com/bitcoinxt/bitcoinxt">Bitcoin XT</a> nodes, which
+ * advertise themselves using the second service bit flag. It requests a query of the UTXO set keyed by a set of
+ * outpoints (i.e. tx hash and output index). The result contains a bitmap of spentness flags, and the contents of
+ * the associated outputs if they were found. The results aren't authenticated by anything, so the peer could lie,
+ * or a man in the middle could swap out its answer for something else.
+ */
 public class GetUTXOsMessage extends Message {
     public static final int MIN_PROTOCOL_VERSION = 70002;
+    /** Bitmask of service flags required for a node to support this command (0x3) */
+    public static final int SERVICE_FLAGS_REQUIRED = 3;
 
     private boolean includeMempool;
     private ImmutableList<TransactionOutPoint> outPoints;