diff --git a/collects/dynext/file-unit.ss b/collects/dynext/file-unit.ss
index 8947a4946d..f790473347 100644
--- a/collects/dynext/file-unit.ss
+++ b/collects/dynext/file-unit.ss
@@ -1,81 +1,64 @@
+#lang scheme/base
 
-(module file-unit mzscheme
-  (require mzlib/unit
-           mzlib/include
-           mzlib/string)
+(require scheme/unit "file-sig.ss")
 
-  (require "file-sig.ss")
+(provide dynext:file@)
 
-  (provide dynext:file@)
+(define-unit dynext:file@ (import) (export dynext:file^)
 
-  (define-unit dynext:file@
-      (import)
-      (export dynext:file^)
+  (define (append-zo-suffix s)
+    (path-add-suffix s #".zo"))
 
-      (define (append-zo-suffix s)
-	(path-add-suffix s #".zo"))
+  (define (append-c-suffix s)
+    (path-add-suffix s #".c"))
 
-      (define (append-c-suffix s)
-	(path-add-suffix s #".c"))
+  (define (append-constant-pool-suffix s)
+    (path-add-suffix s #".kp"))
 
-      (define (append-constant-pool-suffix s)
-	(path-add-suffix s #".kp"))
+  (define (append-object-suffix s)
+    (path-add-suffix s (case (system-type)
+                         [(unix beos macos macosx) #".o"]
+                         [(windows) #".obj"])))
 
-      (define (append-object-suffix s)
-	(path-add-suffix
-	 s
-	 (case (system-type)
-	   [(unix beos macos macosx) #".o"]
-	   [(windows) #".obj"])))
+  (define (append-extension-suffix s)
+    (path-add-suffix s (system-type 'so-suffix)))
 
-      (define (append-extension-suffix s)
-	(path-add-suffix s (system-type 'so-suffix)))
-
-      (define (extract-suffix appender)
-	(subbytes
-	 (path->bytes (appender (bytes->path #"x")))
-	 1))
-
-      (define-values (extract-base-filename/ss
-		      extract-base-filename/c
-		      extract-base-filename/kp
-		      extract-base-filename/o
-		      extract-base-filename/ext)
-	(let ([mk
-	       (lambda (who pat kind simple)
-		 (let ([rx (byte-pregexp
-			    (string->bytes/latin-1 (format "^(.*)\\.(~a)$" pat)))])
-		   (letrec ([extract-base-filename
-			     (case-lambda
-			      [(s p)
-			       (unless (path-string? s)
-				 (raise-type-error who "path or valid-path string" s))
-			       (let ([m (regexp-match rx (path->bytes (if (path? s)
-									  s
-									  (string->path s))))])
-				 (cond
-				  [m (bytes->path (cadr m))]
-				  [p (if simple
-                                         (error p "not a ~a filename (doesn't end with ~a): ~a" kind simple s)
-                                         (path-replace-suffix s #""))]
-				  [else #f]))]
-			      [(s) (extract-base-filename s #f)])])
-		     extract-base-filename)))])
-	  (values
-	   (mk 'extract-base-filename/ss 
-	       #"[sS][sS]|[sS][cC][mM]" "Scheme" #f)
-	   (mk 'extract-base-filename/c
-	       #"[cC]|[cC][cC]|[cC][xX][xX]|[cC][pP][pP]|[cC][+][+]|[mM]" "C" ".c, .cc, .cxx, .cpp, .c++, or .m")
-	   (mk 'extract-base-filename/kp
-	       #"[kK][pP]" "constant pool" ".kp")
-	   (mk 'extract-base-filename/o
-	       (case (system-type)
-		 [(unix beos macos macosx) #"[oO]"]
-		 [(windows) #"[oO][bB][jJ]"])
-	       "compiled object"
-	       (extract-suffix append-object-suffix))
-	   (mk 'extract-base-filename/ext
-               (regexp-quote (subbytes (system-type 'so-suffix) 1) #f)
-	       "MzScheme extension"
-	       (extract-suffix append-extension-suffix)))))))
+  (define (extract-suffix appender)
+    (subbytes (path->bytes (appender (bytes->path #"x"))) 1))
 
+  (define-values (extract-base-filename/ss
+                  extract-base-filename/c
+                  extract-base-filename/kp
+                  extract-base-filename/o
+                  extract-base-filename/ext)
+    (let ([mk
+           (lambda (who pat kind simple)
+             (define rx
+               (byte-pregexp (bytes-append #"^(.*)\\.(?i:" pat #")$")))
+             (define (extract-base-filename s [p #f])
+               (unless (path-string? s)
+                 (raise-type-error who "path or valid-path string" s))
+               (cond [(regexp-match
+                       rx (path->bytes (if (path? s) s (string->path s))))
+                      => (lambda (m) (bytes->path (cadr m)))]
+                     [p (if simple
+                          (error p "not a ~a filename (doesn't end with ~a): ~a"
+                                 kind simple s)
+                          (path-replace-suffix s #""))]
+                     [else #f]))
+             extract-base-filename)])
+      (values
+       (mk 'extract-base-filename/ss #"ss|scm" "Scheme" #f)
+       (mk 'extract-base-filename/c
+           #"c|cc|cxx|cpp|c[+][+]|m" "C" ".c, .cc, .cxx, .cpp, .c++, or .m")
+       (mk 'extract-base-filename/kp #"kp" "constant pool" ".kp")
+       (mk 'extract-base-filename/o
+           (case (system-type)
+             [(unix beos macos macosx) #"o"]
+             [(windows) #"obj"])
+           "compiled object"
+           (extract-suffix append-object-suffix))
+       (mk 'extract-base-filename/ext
+           (regexp-quote (subbytes (system-type 'so-suffix) 1) #f)
+           "MzScheme extension"
+           (extract-suffix append-extension-suffix))))))