diff --git a/src/rk65c02.c b/src/rk65c02.c
index 973c4d8..582eccc 100644
--- a/src/rk65c02.c
+++ b/src/rk65c02.c
@@ -11,18 +11,6 @@
 
 static bool run = false;
 
-struct reg_state {
-	uint8_t A;	/* accumulator */
-	uint8_t X;	/* index X */
-	uint8_t Y;	/* index Y */
-
-	uint16_t PC;	/* program counter */
-	uint8_t SP;	/* stack pointer */
-	uint8_t P;	/* status */
-};
-
-typedef struct reg_state reg_state_t;
-
 instruction_t
 instruction_fetch(bus_t *b, uint16_t addr)
 {
@@ -31,7 +19,7 @@ instruction_fetch(bus_t *b, uint16_t addr)
 	i.opcode = bus_read_1(b, addr);
 	i.def = instrs[i.opcode];
 
-	assert(i.def.op != OP_UNIMPL);
+	assert(i.def.opcode != OP_UNIMPL);
 
 	/* handle operands */		
 	switch (i.def.mode) {
diff --git a/src/rk65c02.h b/src/rk65c02.h
index 6c4f125..d2ac28b 100644
--- a/src/rk65c02.h
+++ b/src/rk65c02.h
@@ -18,8 +18,20 @@ typedef enum {
 	IABSOLUTEX
 } addressing_t;
 
+struct reg_state {
+	uint8_t A;      /* accumulator */
+	uint8_t X;      /* index X */
+	uint8_t Y;      /* index Y */
+
+	uint16_t PC;    /* program counter */
+	uint8_t SP;     /* stack pointer */
+	uint8_t P;      /* status */
+};
+
+typedef struct reg_state reg_state_t;
+
 struct instrdef {
-        uint8_t op;
+        uint8_t opcode;
 	const char *mnemonic;
 	addressing_t mode;
 	uint8_t size;
@@ -36,7 +48,6 @@ struct instruction {
 
 typedef struct instruction instruction_t;
 
-
 #define OP_BRK 0x00
 #define OP_TSB_ZP 0x04
 #define OP_JSR 0x20