diff --git a/classpath/java/util/Hashtable.java b/classpath/java/util/Hashtable.java
index 978847a6b7..9715a42a24 100644
--- a/classpath/java/util/Hashtable.java
+++ b/classpath/java/util/Hashtable.java
@@ -28,7 +28,7 @@ public class Hashtable<K, V> implements Map<K, V> {
     }
   }
 
-  public String toString() {
+  public synchronized String toString() {
     return map.toString();
   }