diff --git a/lib/weakref.rb b/lib/weakref.rb
index ee5444a..3929994 100644
--- a/lib/weakref.rb
+++ b/lib/weakref.rb
@@ -28,21 +28,26 @@ class WeakRef < Delegator
   @@id_rev_map =  {}            # ref -> obj
   @@mutex = Mutex.new
   @@final = lambda {|id|
-    @@mutex.synchronize {
-      rids = @@id_map[id]
-      if rids
-        for rid in rids
-          @@id_rev_map.delete(rid)
+    GC.disable
+    begin
+      @@mutex.synchronize {
+        rids = @@id_map[id]
+        if rids
+          for rid in rids
+            @@id_rev_map.delete(rid)
+          end
+          @@id_map.delete(id)
+        end
+        rid = @@id_rev_map[id]
+        if rid
+          @@id_rev_map.delete(id)
+          @@id_map[rid].delete(id)
+          @@id_map.delete(rid) if @@id_map[rid].empty?
         end
-        @@id_map.delete(id)
-      end
-      rid = @@id_rev_map[id]
-      if rid
-        @@id_rev_map.delete(id)
-        @@id_map[rid].delete(id)
-        @@id_map.delete(rid) if @@id_map[rid].empty?
-      end
-    }
+      }
+    ensure
+      GC.enable
+    end
   }
 
   ##
@@ -52,9 +57,14 @@ class WeakRef < Delegator
     @__id = orig.object_id
     ObjectSpace.define_finalizer orig, @@final
     ObjectSpace.define_finalizer self, @@final
-    @@mutex.synchronize {
-      @@id_map[@__id] = [] unless @@id_map[@__id]
-    }
+    GC.disable
+    begin
+      @@mutex.synchronize {
+        @@id_map[@__id] = [] unless @@id_map[@__id]
+      }
+    ensure
+      GC.enable
+    end
     @@id_map[@__id].push self.object_id
     @@id_rev_map[self.object_id] = @__id
     super