diff --git a/pkgs/racket-doc/scribblings/inside/values.scrbl b/pkgs/racket-doc/scribblings/inside/values.scrbl
index e484fa0f7d..11e9af9c9c 100644
--- a/pkgs/racket-doc/scribblings/inside/values.scrbl
+++ b/pkgs/racket-doc/scribblings/inside/values.scrbl
@@ -186,13 +186,15 @@ types:
  extracts/sets the user data pointer; test for just this type with
  @cppdef{SCHEME_INPORTP}, but use @cppdef{SCHEME_INPUT_PORTP} to recognize
  all input ports (including structures with the
- @racket[prop:input-port] property)}
+ @racket[prop:input-port] property), and use @cppi{scheme_input_port_record}
+ to extract a @cppi{scheme_input_port_type} value from a general input port}
 
  @item{@cppdef{scheme_output_port_type} --- @cppdef{SCHEME_OUTPORT_VAL}
  extracts/sets the user data pointer; test for just this type with
  @cppdef{SCHEME_OUTPORTP}, but use @cppdef{SCHEME_OUTPUT_PORTP} to
  recognize all output ports (including structures with the
- @racket[prop:output-port] property)}
+ @racket[prop:output-port] property), and use @cppi{scheme_output_port_record}
+ to extract a @cppi{scheme_output_port_type} value from a general input port}
 
  @item{@cppdef{scheme_thread_type} --- thread descriptors; test for
  this type with @cppdef{SCHEME_THREADP}}
diff --git a/racket/src/racket/include/scheme.h b/racket/src/racket/include/scheme.h
index 75379d55bd..2182d49a2e 100644
--- a/racket/src/racket/include/scheme.h
+++ b/racket/src/racket/include/scheme.h
@@ -1543,6 +1543,8 @@ struct Scheme_Input_Port
 #endif
 };
 
+#define SCHEME_INPORT_VAL(i) (((Scheme_Input_Port *)i)->port_data)
+
 struct Scheme_Output_Port
 {
   struct Scheme_Port p;
@@ -1566,6 +1568,8 @@ struct Scheme_Output_Port
   struct Scheme_Input_Port *input_half;
 };
 
+#define SCHEME_OUTPORT_VAL(o) (((Scheme_Output_Port *)o)->port_data)
+
 #define SCHEME_SPECIAL (-2)
 #define SCHEME_UNLESS_READY (-3)