diff --git a/src/mos6502/arith.c b/src/mos6502/arith.c
index 62df3b5..8715e3d 100644
--- a/src/mos6502/arith.c
+++ b/src/mos6502/arith.c
@@ -190,14 +190,15 @@ DEFINE_INST(dey)
  */
 DEFINE_INST(inc)
 {
+    oper++;
+    MOS_CHECK_NZ(oper);
+
     if (cpu->addr_mode == ACC) {
-        MOS_CHECK_NZ(cpu->A + 1);
-        cpu->A++;
+        cpu->A = oper;
         return;
     }
 
-    MOS_CHECK_NZ(oper + 1);
-    mos6502_set(cpu, cpu->eff_addr, oper + 1);
+    mos6502_set(cpu, cpu->eff_addr, oper);
 }
 
 /*
@@ -205,8 +206,9 @@ DEFINE_INST(inc)
  */
 DEFINE_INST(inx)
 {
-    MOS_CHECK_NZ(cpu->X + 1);
-    cpu->X++;
+    oper++;
+    MOS_CHECK_NZ(oper);
+    cpu->X = oper;
 }
 
 /*
@@ -214,8 +216,9 @@ DEFINE_INST(inx)
  */
 DEFINE_INST(iny)
 {
-    MOS_CHECK_NZ(cpu->Y + 1);
-    cpu->Y++;
+    oper++;
+    MOS_CHECK_NZ(oper);
+    cpu->Y = oper;
 }
 
 /*