Index: src/org/python/core/PyType.java
===================================================================
--- src/org/python/core/PyType.java	(revision 7066)
+++ src/org/python/core/PyType.java	(working copy)
@@ -1251,9 +1257,11 @@
         return newtype;
     }
 
+    // XXX what's the proper scope of this synchronization? given module import lock, might be
+    // ok to omit this sync here...
     public static synchronized PyType fromClass(Class<?> c) {
         if (class_to_type == null) {
-            class_to_type = Generic.map();
+            class_to_type = Generic.synchronizedWeakHashMap();
             addFromClass(PyType.class, null);
         }
         PyType type = class_to_type.get(c);
Index: src/org/python/util/Generic.java
===================================================================
--- src/org/python/util/Generic.java	(revision 7066)
+++ src/org/python/util/Generic.java	(working copy)
@@ -6,12 +6,14 @@
 import java.util.AbstractSet;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.WeakHashMap;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
@@ -56,6 +58,11 @@
         return new HashMap<K, V>();
     }
 
+    public static <K, V> Map<K, V> synchronizedWeakHashMap() {
+        return Collections.synchronizedMap(new WeakHashMap<K, V>());
+    }
+
+
     /**
      * Makes a ConcurrentMap using generic types inferred from whatever this is being
      * assigned to.