diff --git a/core/java/src/net/i2p/crypto/eddsa/math/bigint/BigIntegerLittleEndianEncoding.java b/core/java/src/net/i2p/crypto/eddsa/math/bigint/BigIntegerLittleEndianEncoding.java
index 06d3fd6a7..e3088daca 100644
--- a/core/java/src/net/i2p/crypto/eddsa/math/bigint/BigIntegerLittleEndianEncoding.java
+++ b/core/java/src/net/i2p/crypto/eddsa/math/bigint/BigIntegerLittleEndianEncoding.java
@@ -15,7 +15,7 @@ public class BigIntegerLittleEndianEncoding extends Encoding implements Serializ
     private BigInteger mask;
 
     @Override
-    public void setField(Field f) {
+    public synchronized void setField(Field f) {
         super.setField(f);
         mask = BigInteger.ONE.shiftLeft(f.getb()-1).subtract(BigInteger.ONE);
     }