diff --git a/collects/mztake/engine.ss b/collects/mztake/engine.ss
index 2a6f145596..d993354632 100644
--- a/collects/mztake/engine.ss
+++ b/collects/mztake/engine.ss
@@ -1,6 +1,9 @@
 (module engine mzscheme
   (require (lib "marks.ss" "mztake" "private")
-           (prefix frp: (lib "frp.ss" "frtime"))
+;           (prefix frp: (lib "frp.ss" "frtime"))
+           (prefix frp: (lib "lang-ext.ss" "frtime"))           
+           (rename (lib "frp-core.ss" "frtime")
+                   frp:signal-thunk signal-thunk)
            (lib "useful-code.ss" "mztake" "private")
            (lib "more-useful-code.ss" "mztake" "private") ; mostly for hash- bindings
            "mztake-structs.ss"
@@ -43,17 +46,18 @@
                                 (cons (unwrap-syntax stx)
                                       (loop (read-syntax filename port)))))
                           (close-input-port port)))))])
-      (lambda (line col)
+      (lambda (line maybe-col)
         (let loop ([lst pos-list]
                    [last-coord (first pos-list)])
           (cond
             ; none is found
             [(empty? lst)
-             (raise (format "No syntax found for trace at line/column ~a:~a in client `~a'" line col filename))]
+             (raise (format "No syntax found for trace at line/column ~a:~a in client `~a'" line maybe-col filename))]
             
             ; if first is correct line and correct column
             [(and (= line (caar lst))
-                  (= col (cadar lst)))
+                  (or (not maybe-col)
+                      (= maybe-col (cadar lst))))
              (third (first lst))]
             
             [else (loop (rest lst)
diff --git a/collects/mztake/mztake-structs.ss b/collects/mztake/mztake-structs.ss
index f16a36e428..9ad5828773 100644
--- a/collects/mztake/mztake-structs.ss
+++ b/collects/mztake/mztake-structs.ss
@@ -1,6 +1,5 @@
 (module mztake-structs mzscheme
-  (require (prefix frp: (lib "frp.ss" "frtime"))
-           (lib "more-useful-code.ss" "mztake" "private"))
+  (require (lib "more-useful-code.ss" "mztake" "private"))
   
   (provide (all-defined-except loc make-loc)
            (rename loc loc$)
diff --git a/collects/mztake/mztake.ss b/collects/mztake/mztake.ss
index c350ed1b0a..1cd1da66fc 100644
--- a/collects/mztake/mztake.ss
+++ b/collects/mztake/mztake.ss
@@ -1,6 +1,6 @@
 (module mztake mzscheme
   (require (lib "contract.ss")
-           (prefix frp: (lib "frp.ss" "frtime"))
+           (prefix frp: (lib "lang-ext.ss" "frtime"))
            (rename (lib "frtime.ss" "frtime") frp:value-nowable? value-nowable?)
            (rename (lib "frtime.ss" "frtime") frp:behaviorof behaviorof)
            "mztake-structs.ss"
@@ -9,14 +9,20 @@
            (lib "marks.ss" "mztake" "private")
            "engine.ss")
   
-  (provide loc$ loc loc-reqspec loc-line loc-col
+  (provide loc$ loc-reqspec loc-line loc-col
            trace trace* bind define/bind define/bind-e where set-main!)
   (provide/contract [kill (() (debug-process?) . opt-> . void?)]
                     [kill-all (-> void?)]
                     [set-running-e! (frp:event? . -> . void?)]
                     [set-running! (frp:value-nowable? . -> . void?)]
                     [exceptions (() (debug-process?) . opt-> . frp:event?)]
-                    [exited? (() (debug-process?) . opt-> . frp:behavior?)])
+                    [exited? (() (debug-process?) . opt-> . frp:behavior?)]
+                    [rename loc/opt-col loc
+                            ((any/c number?) (number?) . opt-> . loc?)])
+  
+  (define loc/opt-col
+    (opt-lambda (reqspec line [col #f])
+      (loc reqspec line col)))
   
   (define exceptions
     (opt-lambda ([p (current-process)])