diff --git a/PDP11/pdp11_sys.c b/PDP11/pdp11_sys.c
index f7528b37..c2b598bb 100644
--- a/PDP11/pdp11_sys.c
+++ b/PDP11/pdp11_sys.c
@@ -379,7 +379,7 @@ static const int32 masks[] = {
 0177700+I_D, 0177400+I_D, 0177700, 0177400,
 0177400, 0177000, 0177000, 0177400,
 0177400+I_D+I_L, 0170000, 0177777, 0177777,
-0177700+I_D, 0177400+I_D, 0177700, 0177400,
+0177000+I_D, 0177400+I_D, 0177700, 0177400,
 0177000, 0177700+I_D, 0177400, 0177400+I_D+I_L
 };