diff --git a/collects/scribblings/reference/namespaces.scrbl b/collects/scribblings/reference/namespaces.scrbl
index 96c4f33dba..8c36ed1fff 100644
--- a/collects/scribblings/reference/namespaces.scrbl
+++ b/collects/scribblings/reference/namespaces.scrbl
@@ -90,7 +90,7 @@ A parameter that determines the @techlink{current namespace}.}
 
 @defproc[(namespace-symbol->identifier [sym symbol?]) identifier?]{
 
-Similar to @scheme[datum->syntax-object] restricted to symbols. The
+Similar to @scheme[datum->syntax] restricted to symbols. The
 lexical context of the resulting identifier corresponds to the
 top-level environment of the current namespace; the identifier has no
 source location or properties.}
diff --git a/collects/scribblings/reference/numbers.scrbl b/collects/scribblings/reference/numbers.scrbl
index 4c330802ea..161caa78ec 100644
--- a/collects/scribblings/reference/numbers.scrbl
+++ b/collects/scribblings/reference/numbers.scrbl
@@ -488,8 +488,9 @@ Returns @scheme[(and (exact-integer? v) (positive? v))].
 @examples[(imag-part 3+4i) (imag-part 5.0) (imag-part 5.0+0.0i)]}
 
 
-@defproc[(magnitude [z number?]) real?]{ Returns the magnitude of
- the complex number @scheme[z] in polar coordinates.
+@defproc[(magnitude [z number?]) (and/c real? (not/c negative?))]{
+ Returns the magnitude of the complex number @scheme[z] in polar
+ coordinates.
 
 @examples[(magnitude -3) (magnitude 3.0) (magnitude 3+4i)]}