diff --git a/src/main/java/com/threerings/io/Streamer.java b/src/main/java/com/threerings/io/Streamer.java
index bd6740298..6afdfafb7 100644
--- a/src/main/java/com/threerings/io/Streamer.java
+++ b/src/main/java/com/threerings/io/Streamer.java
@@ -549,8 +549,10 @@ public abstract class Streamer
             }
 
             // otherwise, ensure the marshallers are initialized and call super
-            if (_marshallers == null) {
-                super.initMarshallers();
+            synchronized (this) {
+                if (_marshallers == null) {
+                    super.initMarshallers();
+                }
             }
             super.writeObject(object, out, useWriter);
         }