diff --git a/bs/TagEngine.bs b/bs/TagEngine.bs
index e1ea262..5b0e5a6 100644
--- a/bs/TagEngine.bs
+++ b/bs/TagEngine.bs
@@ -9,7 +9,8 @@ import Util
 
 interface (TagEngine :: # -> *) numTags =
     requestTag :: ActionValue UIntLog2N(numTags)
-    retireTag  :: UIntLog2N(numTags) -> Action
+    setTagToRetire  :: UIntLog2N(numTags) -> Action
+    retireTag  :: Action
 
 -- The tag engine returns a tag that is unique for the duration of
 -- the lifetime of the tag. Useful when you need to tag transactions
@@ -29,6 +30,9 @@ mkTagEngine =
         stackPtr :: (Reg (Maybe(UIntLog2N(numTags))))
         stackPtr <- mkReg |> Just |> reifiedNumTags - 1
 
+        tagToRetire :: RWire (UIntLog2N(numTags))
+        tagToRetire <- mkRWireSBR
+
         debugOnce <- mkReg True
 
         addRules $
@@ -47,7 +51,7 @@ mkTagEngine =
             requestTag :: ActionValue UIntLog2N(numTags)
             requestTag =
                 do
-                    stackPtr := 
+                    stackPtr :=
                         if sampledStackPtr == 0
                             then Nothing
                             else Just |> sampledStackPtr - 1
@@ -56,16 +60,27 @@ mkTagEngine =
                 when
                     Just sampledStackPtr <- stackPtr
 
-            retireTag :: UIntLog2N(numTags) -> Action
-            retireTag tag = 
+            setTagToRetire  :: UIntLog2N(numTags) -> Action
+            setTagToRetire  tag =
+                let
+                    tagValid = tag < (reifiedNumTags - 1)
+                    tagInUse = readReg (select inUseVec tag)
+                in
+                    do
+                        if (tagValid && tagInUse)
+                            then do tagToRetire.wset tag
+                            else do action {}
+
+            retireTag :: Action
+            retireTag =
                 do
-                    let nextStackPtrUint = 
+                    let nextStackPtrUint =
                             case stackPtr of
                                 Nothing -> 0
                                 Just n -> n + 1
-                    (select inUseVec tag) := False
+
                     (select freeStackVec nextStackPtrUint) := tag
                     stackPtr := Just nextStackPtrUint
-                -- when
-                --     tag < (reifiedNumTags - 1),
-                --     readReg (select inUseVec tag)
+                    (select inUseVec tag) := False
+                when
+                    Valid tag <- tagToRetire.wget