diff --git a/collects/scribble/text/output.ss b/collects/scribble/text/output.ss
index 4e00cda24e..6056ea03b4 100644
--- a/collects/scribble/text/output.ss
+++ b/collects/scribble/text/output.ss
@@ -137,12 +137,17 @@
               (set-mcar! pfxs npfx)  (set-mcdr! pfxs 0)
               (for-each loop c)
               (set-mcar! pfxs pfx) (set-mcdr! pfxs lpfx))]
-           [(prefix)
+           [(prefix) ; maybe call this `add-prefix'?
             (let* ([pfx (mcar pfxs)] [lpfx (mcdr pfxs)]
                    [npfx (pfx+ (pfx+col (pfx+ pfx lpfx)) (car c))])
               (set-mcar! pfxs npfx) (set-mcdr! pfxs 0)
               (for-each loop (cdr c))
               (set-mcar! pfxs pfx) (set-mcdr! pfxs lpfx))]
+           [(set-prefix)
+            (let ([pfx (mcar pfxs)] [lpfx (mcdr pfxs)])
+              (set-mcar! pfxs (car c)) (set-mcdr! pfxs 0)
+              (for-each loop (cdr c))
+              (set-mcar! pfxs pfx) (set-mcdr! pfxs lpfx))]
            [(with-writer)
             (let ([old write])
               (set! write (or (car c) write-string))
@@ -195,6 +200,7 @@
 (define/provide-special (disable-prefix))
 (define/provide-special (restore-prefix))
 (define/provide-special (prefix pfx))
+(define/provide-special (set-prefix pfx))
 (define/provide-special (with-writer writer))
 
 (define make-spaces ; (efficiently)
diff --git a/collects/scribblings/scribble/preprocessor.scrbl b/collects/scribblings/scribble/preprocessor.scrbl
index 0b8ebb87b4..b9f993d4ee 100644
--- a/collects/scribblings/scribble/preprocessor.scrbl
+++ b/collects/scribblings/scribble/preprocessor.scrbl
@@ -1077,7 +1077,7 @@ module's text does.  If you find yourself in such a situation, it is
 better to switch to a Scheme-with-@"@"-expressions file as shown
 above.)
 
-@;FIXME: add more text on `restore-prefix', and on `with-writer'
+@;FIXME: add more text on `restore-prefix', `set-prefix', `with-writer'
 
 @;FIXME: add this to the reference section
 @;@defform[(include filename)]{