diff --git a/forge-game/src/main/java/forge/game/card/Card.java b/forge-game/src/main/java/forge/game/card/Card.java
index 89c1464e0ef..95634a8cf56 100644
--- a/forge-game/src/main/java/forge/game/card/Card.java
+++ b/forge-game/src/main/java/forge/game/card/Card.java
@@ -4603,7 +4603,7 @@ public class Card extends GameEntity implements Comparable<Card> {
      * 
      * @return a {@link java.util.ArrayList} object.
      */
-    public final ArrayList<String> getHiddenExtrinsicKeyword() {
+    public final synchronized ArrayList<String> getHiddenExtrinsicKeyword() {
         while (true) {
             try {
                 final ArrayList<String> keywords = new ArrayList<String>();
@@ -4623,7 +4623,6 @@ public class Card extends GameEntity implements Comparable<Card> {
         }
     }
 
-
     /**
      * <p>
      * addHiddenExtrinsicKeyword.