diff --git a/collects/rackunit/private/check.rkt b/collects/rackunit/private/check.rkt
index fc3e723..3ad4b58 100644
--- a/collects/rackunit/private/check.rkt
+++ b/collects/rackunit/private/check.rkt
@@ -251,7 +251,7 @@
   (equal? expr1 expr2))
 
 (define-simple-check (check-= expr1 expr2 epsilon)
-  (<= (abs (- expr1 expr2)) epsilon))
+  (<= (magnitude (- expr1 expr2)) epsilon))
 
 (define-simple-check (check-true expr)
   (eq? expr #t))
diff --git a/collects/rackunit/scribblings/check.scrbl b/collects/rackunit/scribblings/check.scrbl
index 83850a2..e7ebbbd 100644
--- a/collects/rackunit/scribblings/check.scrbl
+++ b/collects/rackunit/scribblings/check.scrbl
@@ -68,7 +68,7 @@ The following check fails:
 @defproc[(check-= (v1 any) (v2 any) (epsilon number?) (message string? ""))
          void?]{
 
-Checks that @racket[v1] and @racket[v2] are within
+Checks that @racket[v1] and @racket[v2] are numbers within
 @racket[epsilon] of one another.  The optional
 @racket[message] is included in the output if the check
 fails.