diff --git a/sim_serial.c b/sim_serial.c
index 5ac80862..e63c8166 100644
--- a/sim_serial.c
+++ b/sim_serial.c
@@ -205,11 +205,9 @@ for (i=0; i<serial_open_device_count; ++i)
 
 static void sim_error_serial (char *routine, int error)
 {
-extern FILE *sim_debug;
-
 fprintf (stderr, "Serial: %s fails with error %d\n", routine, error);
-if (sim_debug)
-    fprintf (sim_debug, "Serial: %s fails with error %d\n", routine, error);
+if (sim_deb)
+    fprintf (sim_deb, "Serial: %s fails with error %d\n", routine, error);
 return;
 }