diff --git a/collects/compiler/doc.txt b/collects/compiler/doc.txt
index 85bdc6fc55..f8ef3ae233 100644
--- a/collects/compiler/doc.txt
+++ b/collects/compiler/doc.txt
@@ -487,6 +487,11 @@ _embedr-sig.ss_ library provides the signature, _compiler:embed^_.
               the default is 'console for a MzScheme-based application
               and 'windows for a MrEd-based application
 
+      _'single-instance?_ (Windows) - a boolean for MrEd-based apps; the
+              default is #t, which means that the app looks for instances
+              of itself on startup and merely brings the other instance to
+              the front; #f means that multiple instances are expected
+
       _'forget-exe?_ (Windows, Mac OS X) - a boolean; #t for a launcher
               (see `launcher?' below) does not preserve the original
               executable name for `(find-system-path 'exec-file)'; the
diff --git a/collects/compiler/embed-unit.ss b/collects/compiler/embed-unit.ss
index 365c9ba89f..3b5e3ab3c2 100644
--- a/collects/compiler/embed-unit.ss
+++ b/collects/compiler/embed-unit.ss
@@ -91,14 +91,15 @@
 	    exe)))
 
       ;; Find the magic point in the binary:
-      (define (find-cmdline)
-	(let ([m (regexp-match-positions #"\\[Replace me for EXE hack" (current-input-port))])
+      (define (find-cmdline what rx)
+	(let ([m (regexp-match-positions rx (current-input-port))])
 	  (if m
 	      (caar m)
 	      (error 
 	       'make-embedding-executable
 	       (format
-		"can't find cmdline position in executable")))))
+		"can't find ~a position in executable"
+		what)))))
 
       ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
@@ -525,11 +526,25 @@
 					   cmdline)])
 			(if osx?
 			    (finish-osx-mred dest full-cmdline exe keep-exe?)
-			    (let ([cmdpos (with-input-from-file dest-exe find-cmdline)]
+			    (let ([cmdpos (with-input-from-file dest-exe 
+					    (lambda () (find-cmdline 
+							"cmdline"
+							#"\\[Replace me for EXE hack")))]
+				  [anotherpos (and mred?
+						   (eq? 'windows (system-type))
+						   (let ([m (assq 'single-instance? aux)])
+						     (and m (not (cdr m))))
+						   (with-input-from-file dest-exe 
+						     (lambda () (find-cmdline 
+								 "instance-check"
+								 #"yes, please check for another"))))]
 				  [out (open-output-file dest-exe 'update)])
 			      (dynamic-wind
 				  void
 				  (lambda ()
+				    (when anotherpos
+				      (file-position out anotherpos)
+				      (write-bytes #"no," out))
 				    (if long-cmdline?
 					;; write cmdline at end:
 					(file-position out end)
diff --git a/src/mred/mredmsw.cxx b/src/mred/mredmsw.cxx
index 360539f10a..3c39ff17b4 100644
--- a/src/mred/mredmsw.cxx
+++ b/src/mred/mredmsw.cxx
@@ -841,6 +841,9 @@ void MrEdMSWSleep(float secs, void *fds)
   win_extended_fd_set *r, *w, *e;
   DWORD msecs;
 
+  if (fds && ((win_extended_fd_set *)fds)->no_sleep)
+    return;
+
   if (wxCheckMousePosition())
     return;
 
diff --git a/src/mred/mrmain.cxx b/src/mred/mrmain.cxx
index 6ac73a9bb5..ea0b45d25f 100644
--- a/src/mred/mrmain.cxx
+++ b/src/mred/mrmain.cxx
@@ -57,6 +57,12 @@ extern "C" { typedef int (*ACTUAL_MAIN_PTR)(int argc, char **argv); }
 # define CAST_ACTUAL_MAIN /* empty */
 #endif
 
+#ifdef wx_msw
+/* Hack: overwrite "y" with "n" in binary to disable checking for another
+   instance of the same app. */
+char *check_for_another = "yes, please check for another";
+#endif
+
 #if defined(_IBMR2)
 static void dangerdanger(int)
 {
@@ -650,7 +656,7 @@ int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR ignored
   }
 
   /* Check for an existing instance: */
-  {
+  if (check_for_another[0] != 'n') {
     int alreadyrunning;
     HANDLE mutex;