diff --git a/src/code/filesys.lisp b/src/code/filesys.lisp
index 4b93242..34b95f2 100644
--- a/src/code/filesys.lisp
+++ b/src/code/filesys.lisp
@@ -152,52 +152,37 @@
            (make-pattern (pattern))))))
 
 (defun unparse-physical-piece (thing escape-char)
-  (etypecase thing
-    ((member :wild) "*")
-    (simple-string
-     (let* ((srclen (length thing))
-            (dstlen srclen))
-       (dotimes (i srclen)
-         (let ((char (schar thing i)))
-           (case char
-             ((#\* #\? #\[)
-              (incf dstlen))
-             (t (when (char= char escape-char)
-                  (incf dstlen))))))
-       (let ((result (make-string dstlen))
-             (dst 0))
-         (dotimes (src srclen)
-           (let ((char (schar thing src)))
-             (case char
-               ((#\* #\? #\[)
-                (setf (schar result dst) escape-char)
-                (incf dst))
-               (t (when (char= char escape-char)
-                    (setf (schar result dst) escape-char)
-                    (incf dst))))
-             (setf (schar result dst) char)
-             (incf dst)))
-         result)))
-    (pattern
-     (with-simple-output-to-string (s)
-       (dolist (piece (pattern-pieces thing))
-         (etypecase piece
-           (simple-string
-            (write-string piece s))
-           (symbol
-            (ecase piece
-              (:multi-char-wild
-               (write-string "*" s))
-              (:single-char-wild
-               (write-string "?" s))))
-           (cons
-            (case (car piece)
-              (:character-set
-               (write-string "[" s)
-               (write-string (cdr piece) s)
-               (write-string "]" s))
-              (t
-               (error "invalid pattern piece: ~S" piece))))))))))
+  (flet ((write-escaped-simple-string (string escape stream)
+           (dotimes (i (length string))
+             (let ((char (schar string i)))
+               (when (or (char= char escape) (member char '(#\* #\? #\[)))
+                 (write-char escape stream))
+               (write-char char stream)))))
+    (etypecase thing
+      ((member :wild) "*")
+      (simple-string
+       (with-simple-output-to-string (s)
+         (write-escaped-simple-string thing escape-char s)))
+      (pattern
+       (with-simple-output-to-string (s)
+         (dolist (piece (pattern-pieces thing))
+           (etypecase piece
+             (simple-string
+              (write-escaped-simple-string piece escape-char s))
+             (symbol
+              (ecase piece
+                (:multi-char-wild
+                 (write-string "*" s))
+                (:single-char-wild
+                 (write-string "?" s))))
+             (cons
+              (case (car piece)
+                (:character-set
+                 (write-string "[" s)
+                 (write-string (cdr piece) s)
+                 (write-string "]" s))
+                (t
+                 (error "invalid pattern piece: ~S" piece)))))))))))
 
 (defun make-matcher (piece)
   (cond ((eq piece :wild)