diff --git a/prom.h b/prom.h
index 31b4eea..eebe2a7 100644
--- a/prom.h
+++ b/prom.h
@@ -4,7 +4,7 @@
 class prom: public Memory::Device {
 public:
 	virtual void operator= (uint8_t) {}
-	virtual operator uint8_t () { return _mem[_acc]; }
+	virtual operator uint8_t () { return pgm_read_byte(_mem+_acc); }
 
 	prom(const uint8_t *mem, int uint8_ts): Memory::Device(uint8_ts), _mem(mem) {}