diff --git a/PDP1/pdp1_cpu.c b/PDP1/pdp1_cpu.c
index 7d76931d..e4f789d7 100644
--- a/PDP1/pdp1_cpu.c
+++ b/PDP1/pdp1_cpu.c
@@ -1664,7 +1664,7 @@ return SCPE_OK;
 t_stat cpu_show_hist (FILE *st, UNIT *uptr, int32 val, CONST void *desc)
 {
 int32 ov, pf, op, k, di, lnt;
-const char *cptr = (const char *) desc;
+CONST char *cptr = (CONST char *) desc;
 t_stat r;
 InstHistory *h;