diff --git a/pkgs/typed-racket-pkgs/source-syntax/source-syntax.rkt b/pkgs/typed-racket-pkgs/source-syntax/source-syntax.rkt
index db817bf3..2dedd0dd 100644
--- a/pkgs/typed-racket-pkgs/source-syntax/source-syntax.rkt
+++ b/pkgs/typed-racket-pkgs/source-syntax/source-syntax.rkt
@@ -37,25 +37,33 @@
   ;; add-to-table: stx or #f -> stx or #f
   ;; #f as `lookfor` indicates "traverse all of `expanded`
   (define (add-to-table lookfor)
+    ;; stx is expanded syntax, target is source syntax
     (let loop ([stx expanded] [target initial-target])
       (cond
        [(syntax? stx)
-	(define new-target
-	  ;; check if `stx` has the same srcloc as something in orig
-	  ;; in which case it's a good target to use
-	  ;; otherwise keep using the old target
-	  (hash-ref syntax-locs (syntax-loc stx) target))
-	;; map `stx` to the best enclosing syntax we have, if it's not already there
-	(hash-ref! parent-table stx new-target)
-	(cond
-	 ;; if we got what we came for, stop
-	 [(and lookfor (eq? stx lookfor)) new-target]
+        (define new-target
+          ;; check if `stx` has the same srcloc as something in orig
+          ;; in which case it's a good target to use
+          ;; otherwise keep using the old target
+          (hash-ref syntax-locs (syntax-loc stx) target))
+        ;; map `stx` to the best enclosing syntax we have, if it's not already there
+        (hash-ref! parent-table stx new-target)
+        (cond
+         ;; if we got what we came for, stop
+         [(and lookfor (eq? stx lookfor)) new-target]
 
-	 ;; take apart stx and loop on the components
-	 [else
-         (define stxe (syntax-e stx))
-         (and (pair? stxe)
-              (or (loop (car stxe) stx) (loop (cdr stxe) stx)))])]
+         ;; take apart stx and loop on the components
+         [else
+          (let inner ([stxe (syntax-e stx)])
+            (cond [(list? stxe)
+                   (for/or ([x (in-list stxe)])
+                     (loop x new-target))]
+                  [(pair? stxe) ; may be an improper syntax list
+                   (or (loop (car stxe) new-target) (inner (cdr stxe)))]
+                  [(syntax? stxe) ; base case
+                   (loop stxe new-target)]
+                  [else
+                   #f]))])]
        [else #f])))
 
   ;; if now?, add everything to the table