diff --git a/devcmd.c b/devcmd.c
index a5c1bed..0188c94 100644
--- a/devcmd.c
+++ b/devcmd.c
@@ -240,17 +240,14 @@ static int cmd_set(cproc_t cp, char **arg)
 		return -1;
 	}
 
-	while (*reg_text && !isdigit(*reg_text))
-		reg_text++;
-	reg = atoi(reg_text);
-
-	if (expr_eval(stab, val_text, &value) < 0) {
-		fprintf(stderr, "set: can't parse value: %s\n", val_text);
+	reg = dis_reg_from_name(reg_text);
+	if (reg < 0) {
+		fprintf(stderr, "set: unknown register: %s\n", reg_text);
 		return -1;
 	}
 
-	if (reg < 0 || reg >= DEVICE_NUM_REGS) {
-		fprintf(stderr, "set: register out of range: %d\n", reg);
+	if (expr_eval(stab, val_text, &value) < 0) {
+		fprintf(stderr, "set: can't parse value: %s\n", val_text);
 		return -1;
 	}
 
diff --git a/dis.c b/dis.c
index a3c29dc..3814ead 100644
--- a/dis.c
+++ b/dis.c
@@ -526,7 +526,7 @@ const char *dis_opcode_name(msp430_op_t op)
 	return NULL;
 }
 
-msp430_op_t dis_opcode_from_name(const char *name)
+int dis_opcode_from_name(const char *name)
 {
 	int i;
 
@@ -544,19 +544,9 @@ static const char *const msp430_reg_names[] = {
 	"R12", "R13", "R14", "R15"
 };
 
-msp430_reg_t dis_reg_from_name(const char *name)
+int dis_reg_from_name(const char *name)
 {
-	const char *num = name;
-
-	while (num && isdigit(*num))
-		num++;
-
-	if (*num) {
-		msp430_reg_t r = atoi(num);
-
-		if (r >= 0 && r <= 15)
-			return r;
-	}
+	int i;
 
 	if (!strcasecmp(name, "pc"))
 		return 0;
@@ -565,7 +555,18 @@ msp430_reg_t dis_reg_from_name(const char *name)
 	if (!strcasecmp(name, "sr"))
 		return 2;
 
-	return -1;
+	if (toupper(*name) == 'R')
+		name++;
+
+	for (i = 0; name[i]; i++)
+		if (!isdigit(name[i]))
+			return -1;
+
+	i = atoi(name);
+	if (i < 0 || i > 15)
+		return -1;
+
+	return i;
 }
 
 const char *dis_reg_name(msp430_reg_t reg)
diff --git a/dis.h b/dis.h
index 9f45f0d..3575600 100644
--- a/dis.h
+++ b/dis.h
@@ -207,9 +207,9 @@ int dis_decode(const uint8_t *code,
 	       struct msp430_instruction *insn);
 
 /* Look up names for registers and opcodes */
-msp430_op_t dis_opcode_from_name(const char *name);
+int dis_opcode_from_name(const char *name);
 const char *dis_opcode_name(msp430_op_t op);
-msp430_reg_t dis_reg_from_name(const char *name);
+int dis_reg_from_name(const char *name);
 const char *dis_reg_name(msp430_reg_t reg);
 
 #endif
diff --git a/rtools.c b/rtools.c
index dc21ff9..da2f71c 100644
--- a/rtools.c
+++ b/rtools.c
@@ -54,6 +54,7 @@ static int isearch_opcode(cproc_t cp, const char *term, char **arg,
 			  struct isearch_query *q)
 {
 	const char *opname = get_arg(arg);
+	int opc;
 
 	if (q->flags & ISEARCH_OPCODE) {
 		fprintf(stderr, "isearch: opcode already specified\n");
@@ -65,11 +66,12 @@ static int isearch_opcode(cproc_t cp, const char *term, char **arg,
 		return -1;
 	}
 
-	q->insn.op = dis_opcode_from_name(opname);
-	if (q->insn.op < 0) {
+	opc = dis_opcode_from_name(opname);
+	if (opc < 0) {
 		fprintf(stderr, "isearch: unknown opcode: %s\n", opname);
 		return -1;
 	}
+	q->insn.op = opc;
 
 	q->flags |= ISEARCH_OPCODE;
 	return 0;
@@ -170,9 +172,12 @@ static int isearch_reg(cproc_t cp, const char *term, char **arg,
 		return -1;
 	}
 
-	while (*reg_text && !isdigit(*reg_text))
-		reg_text++;
-	reg = atoi(reg_text);
+	reg = dis_reg_from_name(reg_text);
+	if (reg < 0) {
+		fprintf(stderr, "isearch: unknown register: %s\n",
+			reg_text);
+		return -1;
+	}
 
 	q->flags |= which;
 	if (which == ISEARCH_SRC_REG)