diff --git a/cmd/disasm.go b/cmd/disasm.go
index dbfc5e6..0f45bb7 100644
--- a/cmd/disasm.go
+++ b/cmd/disasm.go
@@ -13,24 +13,19 @@ func main() {
 	endString := flag.String("end", "", "End address")
 	flag.Parse()
 
-	startAddress := utils.DecodeCmdLineAddress(startString)
-	endAddress := utils.DecodeCmdLineAddress(endString)
+	start := utils.DecodeCmdLineAddress(startString)
+	end := utils.DecodeCmdLineAddress(endString)
 
-	if startAddress == nil {
+	if start == nil {
 		panic("Must include -start")
 	}
 
-	if endAddress == nil {
+	if end == nil {
 		e := uint16(0xffff)
-		endAddress = &e
+		end = &e
 	}
 
 	cpu.InitInstructionDecoder()
 	mmu.InitApple2eROM()
-
-	cpu.State.PC = *startAddress
-	for cpu.State.PC <= *endAddress {
-		cpu.PrintInstruction(false)
-		cpu.AdvanceInstruction()
-	}
+	utils.Disassemble(*start, *end)
 }
diff --git a/cpu/cpu.go b/cpu/cpu.go
index 081ae99..e4d51cf 100644
--- a/cpu/cpu.go
+++ b/cpu/cpu.go
@@ -851,7 +851,7 @@ func Run(showInstructions bool, breakAddress *uint16, exitAtBreak bool, disableF
 			postProcessIncDec(addressMode)
 
 		default:
-			fmt.Printf("Unknown opcode $%02x\n", opcode)
+			fmt.Printf("Unknown opcode $%02x at %04x\n", opcode, State.PC)
 			return
 		}
 	}
diff --git a/utils/utils.go b/utils/utils.go
index e8e7d70..0c54a25 100644
--- a/utils/utils.go
+++ b/utils/utils.go
@@ -60,3 +60,15 @@ func RunUntilBreakPoint(t *testing.T, breakAddress uint16, seconds int, showInst
 		t.Fatalf("Did not reach breakpoint at %04x. Got to %04x", breakAddress, cpu.State.PC)
 	}
 }
+
+func Disassemble(start uint16, end uint16) {
+	oldPC := cpu.State.PC
+
+	cpu.State.PC = start
+	for cpu.State.PC <= end {
+		cpu.PrintInstruction(false)
+		cpu.AdvanceInstruction()
+	}
+
+	cpu.State.PC = oldPC
+}