diff --git a/collects/handin-server/checker.ss b/collects/handin-server/checker.ss
index e7ee140042..ff6ca9c201 100644
--- a/collects/handin-server/checker.ss
+++ b/collects/handin-server/checker.ss
@@ -174,9 +174,9 @@
 
 (define (submission->bytes submission maxwidth textualize? untabify?
                            markup-prefix bad-re)
-  (define magic #"WXME")
-  (unless (equal? magic (subbytes submission 0 (bytes-length magic)))
-    (error* "bad submission format, expecting a single  DrScheme submission"))
+  (define magic #rx#"^(?:#reader[(]lib\"read.ss\"\"wxme\"[)])?WXME")
+  (unless (regexp-match? magic submission)
+    (error* "bad submission format, expecting a single DrScheme submission"))
   (let-values ([(defs inters) (unpack-submission submission)])
     (parameterize ([current-input-port
                     (if textualize?
diff --git a/collects/handin-server/doc.txt b/collects/handin-server/doc.txt
index 961e37ca6a..19d0b5d5c0 100644
--- a/collects/handin-server/doc.txt
+++ b/collects/handin-server/doc.txt
@@ -645,6 +645,9 @@ _utils.ss_
   submission byte string.  The byte string is opened for reading, with
   line-counting enabled.
 
+  See the "sandbox.ss" MzLib library for information on
+  `make-evaluator'.
+
 > (call-with-evaluator language teachpack-paths input-program proc)
   Calls `proc' with an evaluator for the given language, teachpack
   paths, and initial definition content as supplied by input-program
@@ -788,13 +791,13 @@ Keywords for configuring `check:':
   "utils.ss").
 
 * :language -- the language that is used for evaluating submissions,
-  same as the `language' argument for `make-evaluator' (see above).
-  There is no default for this, so it must be set or an error is
-  raised.
+  same as the `language' argument for `make-evaluator' (see
+  "sandbox.ss").  There is no default for this, so it must be set or
+  an error is raised.
 
 * :teachpacks -- teachpacks for evaluating submissions, same as the
-  `teachpacks' argument for `make-evaluator' (see above).  Defaults to
-  null -- no teachpacks.
+  `teachpacks' argument for `make-evaluator' (see "sandbox.ss").
+  Defaults to null -- no teachpacks.
 
 * :create-text? -- if true, then a textual version of the submission
   is saved as "text.scm" in a "grading" subdirectory (or any suffix