diff --git a/collects/drscheme/private/debug.ss b/collects/drscheme/private/debug.ss
index 8a5f50bdc3..d1558405b9 100644
--- a/collects/drscheme/private/debug.ss
+++ b/collects/drscheme/private/debug.ss
@@ -693,7 +693,7 @@ profile todo:
                    (< (send from-text get-snip-position snip) para-end-pos))
           (send to-text insert (send snip copy))
           (loop (send snip next))))
-      (send to-text highlight-range (- from-start 1) from-end (get-error-color) #f #f 'high)
+      (send to-text highlight-range (max 0 (- from-start 1)) from-end (get-error-color) #f #f 'high)
       to-text))
   
   ;; get-filename : debug-source -> string