diff --git a/collects/compiler/zo-parse.rkt b/collects/compiler/zo-parse.rkt
index 468c27fe21..6c9493537b 100644
--- a/collects/compiler/zo-parse.rkt
+++ b/collects/compiler/zo-parse.rkt
@@ -307,7 +307,7 @@
                                 [else (error 'zo-parse "bad phase ~a body element: ~e" i sb)]))))
                     ;; unexported:
                     (for/list ([l (in-list phase-data)]
-                               #:when (not (void? (list-ref l 1))))
+                               #:unless (void? (list-ref l 1)))
                       (let* ([phase (list-ref l 0)]
                              [indirect-syntax 
                               ;; could check: (list-ref l 2) should be size of vector:
diff --git a/collects/profile/render-text.rkt b/collects/profile/render-text.rkt
index 61f21f31d4..a341ed2a90 100644
--- a/collects/profile/render-text.rkt
+++ b/collects/profile/render-text.rkt
@@ -122,8 +122,8 @@
       (define (sub get-edges get-node get-node-time)
         (for*/list ([edge (in-list (get-edges node))]
                     [sub  (in-list (list (get-node edge)))] ; <-- hack...
-                    #:when (not (or (eq? *-node sub)        ; <-- ...for this
-                                    (memq sub hidden))))
+                    #:unless (or (eq? *-node sub)           ; <-- ...for this
+                                 (memq sub hidden)))
           (define name   (node-> 'sub-label sub))
           (define local% (format-percent (get-node-time edge) total))
           `("" "" "" "" "" "" "" ""
diff --git a/collects/racket/vector.rkt b/collects/racket/vector.rkt
index e53e8e47e9..c8717a5f7b 100644
--- a/collects/racket/vector.rkt
+++ b/collects/racket/vector.rkt
@@ -123,7 +123,7 @@
 
 (define (vector-filter-not f v)
   (one-arg-check f v 'vector-filter-not)
-  (list->vector (for/list ([i (in-vector v)] #:when (not (f i))) i)))
+  (list->vector (for/list ([i (in-vector v)] #:unless (f i)) i)))
 
 (define (vector-count f v . vs)
   (unless (and (procedure? f) (procedure-arity-includes? f (add1 (length vs))))
diff --git a/collects/rackunit/docs-complete.rkt b/collects/rackunit/docs-complete.rkt
index 97b06fdd05..d712336470 100644
--- a/collects/rackunit/docs-complete.rkt
+++ b/collects/rackunit/docs-complete.rkt
@@ -74,13 +74,8 @@
   
   (define undocumented-exports
     (for/list ([ex (in-list exports)]
-               #:when
-               (not (xref-binding->definition-tag
-                     xref
-                     (list what ex)
-                     #f))
-               #:when
-               (not (skip-proc ex)))
+               #:unless (xref-binding->definition-tag xref (list what ex) #f)
+               #:unless (skip-proc ex))
       ex))
   
   (unless (null? undocumented-exports)
diff --git a/collects/setup/scribble.rkt b/collects/setup/scribble.rkt
index cc76f5be36..256dadb79e 100644
--- a/collects/setup/scribble.rkt
+++ b/collects/setup/scribble.rkt
@@ -290,7 +290,7 @@
             (set-info-need-run?! info #t))))
       ;; If any expected dependency changed, then we need a re-run:
       (for ([i infos]
-            #:when (not (or (info-need-run? i) (not (info-build? i)))))
+            #:unless (or (info-need-run? i) (not (info-build? i))))
         (let ([ch (ormap (lambda (i2)
                            (or (and (not (info? i2))
                                     i2)
diff --git a/collects/syntax/parse/private/rep-data.rkt b/collects/syntax/parse/private/rep-data.rkt
index 50cf81f022..b43f38ac74 100644
--- a/collects/syntax/parse/private/rep-data.rkt
+++ b/collects/syntax/parse/private/rep-data.rkt
@@ -201,7 +201,7 @@ expressions are duplicated, and may be evaluated in different scopes.
   (for ([id (in-list ids)]) (bound-id-table-set! idbm id #t))
   (for/list ([(k v) (in-dict (declenv-table env))]
              #:when (or (den:class? v) (den:magic-class? v) (den:parser? v))
-             #:when (not (bound-id-table-ref idbm k #f)))
+             #:unless (bound-id-table-ref idbm k #f))
     k))
 
 ;; Conventions = (listof (list regexp DeclEntry))
diff --git a/collects/tests/scribble/reader.rkt b/collects/tests/scribble/reader.rkt
index bbc4ac3e16..0b5c100649 100644
--- a/collects/tests/scribble/reader.rkt
+++ b/collects/tests/scribble/reader.rkt
@@ -932,7 +932,7 @@ END-OF-TESTS
            ;; split the tests
            [ts (regexp-split #px"(?m:^)-+(?:$|\r?\n)" ts)])
       (parameterize ([port-count-lines-enabled #t])
-        (for ([t ts] #:when (not (regexp-match? #px"^\\s*$" t)))
+        (for ([t ts] #:unless (regexp-match? #px"^\\s*$" t))
           (let ([m (or (regexp-match #px"^(.*)\n\\s*(-\\S+->)\\s*\n(.*)$"
                                      t)
                        (regexp-match #px"^(.*\\S)\\s+(-\\S+->)\\s+(\\S.*)$"
diff --git a/collects/tests/unstable/helpers.rkt b/collects/tests/unstable/helpers.rkt
index 439e7d302a..3f536562f2 100644
--- a/collects/tests/unstable/helpers.rkt
+++ b/collects/tests/unstable/helpers.rkt
@@ -67,7 +67,7 @@
                     [actuals expecteds]
                     ([actual (in-list actual-sorted)]
                      [expected (in-list actual-sorted)]
-                     #:when (not (== actual expected)))
+                     #:unless (== actual expected))
                   (values actual expected))])
             (unless (and (null? actuals) (null? expecteds))
               (with-check-info*
diff --git a/collects/typed-racket/env/type-env-structs.rkt b/collects/typed-racket/env/type-env-structs.rkt
index 30c6b04849..2b346992c2 100644
--- a/collects/typed-racket/env/type-env-structs.rkt
+++ b/collects/typed-racket/env/type-env-structs.rkt
@@ -41,8 +41,8 @@
     [(env l)
      (mk-env e
              (for/fold ([h l])
-               ([(k v) (in-dict l)]
-                #:when (not (f (cons k v))))
+                       ([(k v) (in-dict l)]
+                        #:unless (f (cons k v)))
                (dict-remove h k)))]))
 
 (r:define/cond-contract (make-empty-env dict)
diff --git a/collects/typed-racket/optimizer/float.rkt b/collects/typed-racket/optimizer/float.rkt
index 66022808f3..ed663f7e60 100644
--- a/collects/typed-racket/optimizer/float.rkt
+++ b/collects/typed-racket/optimizer/float.rkt
@@ -116,7 +116,7 @@
                       (log-float-real-missed-opt
                        this-syntax
                        (for/list ([x (in-list (syntax->list #'(f1 f2 fs ...)))]
-                                  #:when (not (subtypeof? x -Flonum)))
+                                  #:unless (subtypeof? x -Flonum))
                          x)))
                     ;; If an optimization was expected (whether it was safe or not doesn't matter),
                     ;; report subexpressions doing expensive exact arithmetic (Exact-Rational and
diff --git a/collects/typed-racket/typecheck/tc-app.rkt b/collects/typed-racket/typecheck/tc-app.rkt
index 7f6744a9c9..b93a451d28 100644
--- a/collects/typed-racket/typecheck/tc-app.rkt
+++ b/collects/typed-racket/typecheck/tc-app.rkt
@@ -177,7 +177,7 @@
                [pt (in-list pos-tys)])
            (tc-expr/check pa (ret pt)))
          (for ([n names]
-               #:when (not (memq n tnames)))
+               #:unless (memq n tnames))
            (tc-error/delayed
             "unknown named argument ~a for class\nlegal named arguments are ~a"
             n (stringify tnames)))
diff --git a/collects/typed-racket/types/filter-ops.rkt b/collects/typed-racket/types/filter-ops.rkt
index eaaa9ef0ee..682315a2d3 100644
--- a/collects/typed-racket/types/filter-ops.rkt
+++ b/collects/typed-racket/types/filter-ops.rkt
@@ -163,10 +163,9 @@
            (let-values ([(atomic not-atomic) (partition atomic-filter? result)])
              (define not-atomic*
                (for/list ([p (in-list not-atomic)]
-                          #:when
-                          (not (for/or ([a (in-list atomic)])
-                                       (implied-atomic? p a))))
-                         p))
+                          #:unless (for/or ([a (in-list atomic)])
+                                     (implied-atomic? p a)))
+                 p))
              ;; `compact' takes care of implications between atomic props
              (apply mk (compact (append not-atomic* atomic) #f)))])
         (match (car fs)
diff --git a/collects/unstable/define.rkt b/collects/unstable/define.rkt
index 9b2b3f1cf2..b58870fbde 100644
--- a/collects/unstable/define.rkt
+++ b/collects/unstable/define.rkt
@@ -79,7 +79,7 @@
   (syntax-case stx []
     [(_ def [name ...] expr)
      (let* ([ids (syntax->list #'(name ...))])
-       (for ([bad (in-list ids)] #:when (not (identifier? bad)))
+       (for ([bad (in-list ids)] #:unless (identifier? bad))
          (wrong-syntax bad "expected an identifier"))
        (let*-values ([(bound unbound) (partition identifier-binding ids)])
          (cond
diff --git a/collects/unstable/gui/pict.rkt b/collects/unstable/gui/pict.rkt
index 577a9dfd13..058267e5e4 100644
--- a/collects/unstable/gui/pict.rkt
+++ b/collects/unstable/gui/pict.rkt
@@ -160,7 +160,7 @@
     [(_ [name ...] body ...)
      (let* ([ids (syntax->list #'(name ...))])
 
-       (for ([id (in-list ids)] #:when (not (identifier? id)))
+       (for ([id (in-list ids)] #:unless (identifier? id))
          (raise-syntax-error #f "expected an identifier" stx id))
 
        (with-syntax ([(num ...)