diff --git a/bepascal/source/bepascal/pas/src/be/kernel/os.pp b/bepascal/source/bepascal/pas/src/be/kernel/os.pp
index 68464bf..1945932 100644
--- a/bepascal/source/bepascal/pas/src/be/kernel/os.pp
+++ b/bepascal/source/bepascal/pas/src/be/kernel/os.pp
@@ -132,7 +132,7 @@ function write_port(port : port_id; code : Longint; const buf : Pointer;
                     buf_size : size_t)
          : status_t; cdecl; external 'root' name 'write_port';
 
-function read_port(port : port_id; code : Longint; buf : Pointer;
+function read_port(port : port_id; var code : Longint; buf : Pointer;
                    buf_size : size_t)
          : status_t; cdecl; external 'root' name 'read_port';
 
@@ -731,4 +731,4 @@ initialization
   B_INFINITE_TIMEOUT := Int64($7FFFFFFF) shl 32 + Int64($FFFFFFFF);
 {$endif VER1_0}
 
-end.
\ No newline at end of file
+end.