diff --git a/collects/drscheme/private/rep.ss b/collects/drscheme/private/rep.ss
index 340c56a737..650115d5a0 100644
--- a/collects/drscheme/private/rep.ss
+++ b/collects/drscheme/private/rep.ss
@@ -893,14 +893,17 @@ TODO
              (ask-about-kill? #f))
       (define/public (get-in-evaluation?) in-evaluation?)
       
-      (define/private (insert-warning message)
-        (begin-edit-sequence)
-        (let ([start (get-insertion-point)])
-          (insert-before message)
-          (let ([end (get-insertion-point)])
-            (change-style warning-style-delta start end)))
-        (insert-before "\n")
-        (end-edit-sequence))
+      (define/public-final (insert-warning message)
+        (let ([locked? (is-locked?)])
+          (when locked? (lock #f))
+          (begin-edit-sequence)
+          (let ([start (get-insertion-point)])
+            (insert-before message)
+            (let ([end (get-insertion-point)])
+              (change-style warning-style-delta start end)))
+          (insert-before "\n")
+          (end-edit-sequence)
+          (when locked? (lock #t))))
       
       (field (already-warned? #f)
              (show-no-user-evaluation-message? #t))