diff --git a/VAX/vax_cpu1.c b/VAX/vax_cpu1.c
index 869dbf3c..ae483ab5 100644
--- a/VAX/vax_cpu1.c
+++ b/VAX/vax_cpu1.c
@@ -1434,8 +1434,8 @@ return 0;
 
 int32 op_mtpr (int32 *opnd)
 {
-int32 val = opnd[0];
-int32 prn = opnd[1];
+uint32 val = (uint32)opnd[0];
+uint32 prn = (uint32)opnd[1];
 int32 cc;
 
 if (PSL & PSL_CUR)                                      /* must be kernel */