diff --git a/collects/ffi/objc.scrbl b/collects/ffi/objc.scrbl
index e4564f6161..6a5d0c810a 100644
--- a/collects/ffi/objc.scrbl
+++ b/collects/ffi/objc.scrbl
@@ -118,13 +118,13 @@ Defines each @scheme[class-id] to the class (a value with FFI type
 (eval:alts (import-class NSString) (void))
 ]}
 
-@defform/subs[#:literals (+ -)
+@defform/subs[#:literals (+ - +a -a)
               (define-objc-class class-id superclass-expr
                 [field-id ...]
                 method)
               ([method (mode result-ctype-expr (method-id) body ...+)
                        (mode result-ctype-expr (arg ...+) body ...+)]
-               [mode + -]
+               [mode + - +a -a]
                [arg (code:line method-id [ctype-expr arg-id])])]{
 
 Defines @scheme[class-id] as a new, registered Objective-C class (of
@@ -138,10 +138,12 @@ directly when the method @scheme[body]s. Outside the object, they can
 be referenced and set with @scheme[get-ivar] and @scheme[set-ivar!].
 
 Each @scheme[method] adds or overrides a method to the class (when
-@scheme[mode] is @scheme[-]) to be called on instances, or it adds a
-method to the meta-class (when @scheme[mode] is @scheme[+]) to be
-called on the class itself. All result and argument types must be
-declared using FFI C types (@seeCtype).
+@scheme[mode] is @scheme[-] or @scheme[-a]) to be called on instances,
+or it adds a method to the meta-class (when @scheme[mode] is
+@scheme[+] or @scheme[+a]) to be called on the class itself. All
+result and argument types must be declared using FFI C types
+(@seeCtype). When @scheme[mode] is @scheme[+a] or @scheme[-a], the
+method is called in atomic mode (see @scheme[_cprocedure]).
 
 If a @scheme[method] is declared with a single @scheme[method-id] and
 no arguments, then @scheme[method-id] must not end with
diff --git a/collects/ffi/objc.ss b/collects/ffi/objc.ss
index 0b89fb3eb9..bf6884b2c1 100644
--- a/collects/ffi/objc.ss
+++ b/collects/ffi/objc.ss
@@ -364,7 +364,7 @@
                                 ;; Given a dealloc extension:
                                 #'()
                                 ;; Need to add one explicitly:
-                                #'((- _void (dealloc) (void)))))])
+                                #'((-a _void (dealloc) (void)))))])
            (syntax/loc stx
              (begin
                (define superclass-id superclass)
@@ -454,10 +454,13 @@
        (syntax-case #'m ()
          [(kind result-type (id arg ...) body0 body ...)
           (or (free-identifier=? #'kind #'+)
-              (free-identifier=? #'kind #'-))
+              (free-identifier=? #'kind #'-)
+              (free-identifier=? #'kind #'+a)
+              (free-identifier=? #'kind #'-a))
           (let ([id #'id]
                 [args (syntax->list #'(arg ...))]
-                [in-class? (free-identifier=? #'kind #'+)])
+                [in-class? (or (free-identifier=? #'kind #'+)
+                               (free-identifier=? #'kind #'+a))])
             (when (null? args)
               (unless (identifier? id)
                 (raise-syntax-error #f
@@ -485,7 +488,9 @@
                                  '())]
                             [in-cls (if in-class?
                                         #'(object_getClass cls)
-                                        #'cls)])
+                                        #'cls)]
+                            [atomic? (or (free-identifier=? #'kind #'+a)
+                                         (free-identifier=? #'kind #'-a))])
                 (syntax/loc stx
                   (let ([rt result-type]
                         [arg-id arg-type] ...)
@@ -498,7 +503,7 @@
                                                                     [super-tell do-super-tell])
                                                 body0 body ...
                                                 dealloc-body ...)))
-                                           (_fun _id _id arg-type ... -> rt)
+                                           (_fun #:atomic? atomic? _id _id arg-type ... -> rt)
                                            (generate-layout rt (list arg-id ...)))))))))]
          [else (raise-syntax-error #f
                                    "bad method form"
diff --git a/collects/scribblings/foreign/types.scrbl b/collects/scribblings/foreign/types.scrbl
index cdd5afabc5..b0bac7395d 100644
--- a/collects/scribblings/foreign/types.scrbl
+++ b/collects/scribblings/foreign/types.scrbl
@@ -334,7 +334,7 @@ this procedure type and called from foreign code, then the PLT Scheme
 process is put into atomic mode while evaluating the Scheme procedure
 body. In atomic mode, other Scheme threads do not run, so the Scheme
 code must not call any function that potentially synchronizes with
-other threads, otherwise it may deadlock. In addition, the Scheme code
+other threads, or else it may deadlock. In addition, the Scheme code
 must not perform any potentially blocking operation (such as I/O), it
 must not raise an uncaught exception, it must not perform any escaping
 continuation jumps, and its non-tail recursion must be minimal to
diff --git a/collects/scribblings/reference/booleans.scrbl b/collects/scribblings/reference/booleans.scrbl
index 60d36ac334..33c1738fee 100644
--- a/collects/scribblings/reference/booleans.scrbl
+++ b/collects/scribblings/reference/booleans.scrbl
@@ -128,7 +128,9 @@ type. The property value must be a list of three procedures:
         @scheme[equal?] to ensure that data cycles are handled
         properly and to work with @scheme[equal?/recur] (but beware
         that an arbitrary function can be provided to
-        @scheme[equal?/recur]).
+        @scheme[equal?/recur] for recursive checks, which means that
+        arguments provided to the predicate might be exposed to
+        arbitrary code).
 
         The @scheme[_equal-proc] is called for a pair of structures
         only when they are not @scheme[eq?], and only when they both