Index: library.scm
===================================================================
--- library.scm	(Revision 11663)
+++ library.scm	(Arbeitskopie)
@@ -1944,12 +1944,12 @@
     (lambda (str thunk . mode)
       (let ((old ##sys#standard-input)
 	    (file (apply open-input-file str mode)) )
-	(set! ##sys#standard-input file)
-	(##sys#call-with-values thunk
-	  (lambda results
-	    (close-input-port file)
-	    (set! ##sys#standard-input old)
-	    (apply ##sys#values results) ) ) ) ) ) )
+	(fluid-let ([##sys#standard-input file])
+          (##sys#call-with-values thunk
+	    (lambda results
+	      (close-input-port file)
+	      (set! ##sys#standard-input old)
+	      (apply ##sys#values results) ) )) ) ) ) )
 
 (define with-output-to-file 
   (let ((open-output-file open-output-file)
@@ -1957,12 +1957,12 @@
     (lambda (str thunk . mode)
       (let ((old ##sys#standard-output)
 	    (file (apply open-output-file str mode)) )
-	(set! ##sys#standard-output file)
-	(##sys#call-with-values thunk
-	  (lambda results
-	    (close-output-port file)
-	    (set! ##sys#standard-output old)
-	    (apply ##sys#values results) ) ) ) ) ) )
+	(fluid-let ([##sys#standard-output file])
+	  (##sys#call-with-values thunk
+	    (lambda results
+	      (close-output-port file)
+	      (set! ##sys#standard-output old)
+	      (apply ##sys#values results) ) )) ) ) ) )
 
 (define (file-exists? name)
   (##sys#check-string name 'file-exists?)