diff --git a/collects/mysterx/mxdemo.ss b/collects/mysterx/mxdemo.ss
index 29acbcd1a8..a462bd23de 100644
--- a/collects/mysterx/mxdemo.ss
+++ b/collects/mysterx/mxdemo.ss
@@ -17,8 +17,8 @@
   (define-runtime-path myspage-dll '(so "myspage"))
   (define-runtime-path myssink-dll '(so "myssink"))
   ;; Register them every time we start:
-  (system* "regsvr32.exe" "/s" myspage-dll)
-  (system* "regsvr32.exe" "/s" myssink-dll)
+  (system* "regsvr32.exe" "/s" (path->string myspage-dll))
+  (system* "regsvr32.exe" "/s" (path->string myssink-dll))
 
   ; the browser with the calendar