diff --git a/src/main.c b/src/main.c
index 85770ef..5bc3222 100644
--- a/src/main.c
+++ b/src/main.c
@@ -88,14 +88,14 @@ struct action {
 };
 
 static struct action actions[] = {
-	{ "getgpr",  "<gpr>", "Read General Purpose Register (GPR)", &handle_gpr },
-	{ "putgpr",  "<gpr> <value>", "Write General Purpose Register (GPR)", &handle_gpr },
-	{ "getnia",  "", "Get Next Instruction Address (NIA)", &handle_nia },
-	{ "putnia",  "<value>", "Write Next Instrution Address (NIA)", &handle_nia },
-	{ "getspr",  "<spr>", "Get Special Purpose Register (SPR)", &handle_spr },
-	{ "putspr",  "<spr> <value>", "Write Special Purpose Register (SPR)", &handle_spr },
-	{ "getmsr",  "", "Get Machine State Register (MSR)", &handle_msr },
-	{ "putmsr",  "<value>", "Write Machine State Register (MSR)", &handle_msr },
+	{ "getgpr",  "<gpr>", "Read General Purpose Register (GPR)", &handle_getgpr },
+	{ "putgpr",  "<gpr> <value>", "Write General Purpose Register (GPR)", &handle_putgpr },
+	{ "getnia",  "", "Get Next Instruction Address (NIA)", &handle_getnia },
+	{ "putnia",  "<value>", "Write Next Instrution Address (NIA)", &handle_putnia },
+	{ "getspr",  "<spr>", "Get Special Purpose Register (SPR)", &handle_getspr },
+	{ "putspr",  "<spr> <value>", "Write Special Purpose Register (SPR)", &handle_putspr },
+	{ "getmsr",  "", "Get Machine State Register (MSR)", &handle_getmsr },
+	{ "putmsr",  "<value>", "Write Machine State Register (MSR)", &handle_putmsr },
 	{ "getring", "<addr> <len>", "Read a ring. Length must be correct", &handle_getring },
 	{ "start",   "", "Start thread", &thread_start },
 	{ "step",    "<count>", "Set a thread <count> instructions", &thread_step },
diff --git a/src/reg.c b/src/reg.c
index 002cfe9..932ae43 100644
--- a/src/reg.c
+++ b/src/reg.c
@@ -91,10 +91,10 @@ static int getprocreg(struct pdbg_target *target, uint32_t index, uint64_t *reg,
 	return !rc;
 }
 
-int handle_gpr(int optind, int argc, char *argv[])
+static int parse_gpr(int optind, int argc, char *argv[])
 {
 	char *endptr;
-	uint64_t gpr;
+	int gpr;
 
 	if (optind + 1 >= argc) {
 		printf("%s: command '%s' requires a GPR\n", argv[0], argv[optind]);
@@ -102,10 +102,10 @@ int handle_gpr(int optind, int argc, char *argv[])
 	}
 
 	errno = 0;
-	gpr = strtoull(argv[optind + 1], &endptr, 0);
+	gpr = strtoul(argv[optind + 1], &endptr, 0);
 	if (errno || *endptr != '\0') {
 		printf("%s: command '%s' couldn't parse GPR '%s'\n",
-				argv[0], argv[optind], argv[optind + 1]);
+		       argv[0], argv[optind], argv[optind + 1]);
 		return -1;
 	}
 
@@ -114,120 +114,134 @@ int handle_gpr(int optind, int argc, char *argv[])
 		return -1;
 	}
 
-	if (strcmp(argv[optind], "putgpr") == 0) {
-		uint64_t data;
+	return gpr;
+}
 
-		if (optind + 2 >= argc) {
-			printf("%s: command '%s' requires data\n", argv[0], argv[optind]);
-			return -1;
-		}
+static int parse_data(int optind, int argc, char *argv[], uint64_t *data)
+{
+	char *endptr;
 
-		errno = 0;
-		data = strtoull(argv[optind + 2], &endptr, 0);
-		if (errno || *endptr != '\0') {
-			printf("%s: command '%s' couldn't parse data '%s'\n",
-				argv[0], argv[optind], argv[optind + 1]);
-			return -1;
-		}
+	if (optind + 2 >= argc) {
+		printf("%s: command '%s' requires data\n", argv[0], argv[optind]);
+		return -1;
+	}
 
-		return for_each_target("thread", putprocreg, &gpr, &data);
+	errno = 0;
+	*data = strtoull(argv[optind + 2], &endptr, 0);
+	if (errno || *endptr != '\0') {
+		printf("%s: command '%s' couldn't parse data '%s'\n",
+		       argv[0], argv[optind], argv[optind + 1]);
+		return -1;
 	}
 
+	return 0;
+}
+
+int handle_getgpr(int optind, int argc, char *argv[])
+{
+	uint64_t gpr;
+
+	if ((gpr = parse_gpr(optind, argc, argv)) < 0)
+		return -1;
+
 	return for_each_target("thread", getprocreg, &gpr, NULL);
 }
 
-int handle_nia(int optind, int argc, char *argv[])
+int handle_putgpr(int optind, int argc, char *argv[])
 {
-	uint64_t reg = REG_NIA;
-	char *endptr;
+	uint64_t gpr, data;
 
-	if (strcmp(argv[optind], "putnia") == 0) {
-		uint64_t data;
+	if ((gpr = parse_gpr(optind, argc, argv)) < 0)
+		return -1;
 
-		if (optind + 2 >= argc) {
-			printf("%s: command '%s' requires data\n", argv[0], argv[optind]);
-			return -1;
-		}
+	if (parse_data(optind, argc, argv, &data))
+		return -1;
 
-		errno = 0;
-		data = strtoull(argv[optind + 2], &endptr, 0);
-		if (errno || *endptr != '\0') {
-			printf("%s: command '%s' couldn't parse data '%s'\n",
-				argv[0], argv[optind], argv[optind + 1]);
-			return -1;
-		}
+	return for_each_target("thread", putprocreg, &gpr, &data);
+}
 
-		return for_each_target("thread", putprocreg, &reg, &data);
-	}
+int handle_getnia(int optind, int argc, char *argv[])
+{
+	uint64_t reg = REG_NIA;
 
 	return for_each_target("thread", getprocreg, &reg, NULL);
 }
 
-int handle_spr(int optind, int argc, char *argv[])
+int handle_putnia(int optind, int argc, char *argv[])
+{
+	uint64_t reg = REG_NIA, data;
+
+	if (parse_data(optind, argc, argv, &data))
+		return -1;
+
+	return for_each_target("thread", putprocreg, &reg, &data);
+}
+
+static int parse_spr(int optind, int argc, char *argv[])
 {
 	char *endptr;
-	uint64_t spr;
+	int gpr;
 
 	if (optind + 1 >= argc) {
-		printf("%s: command '%s' requires a GPR\n", argv[0], argv[optind]);
+		printf("%s: command '%s' requires a SPR\n", argv[0], argv[optind]);
 		return -1;
 	}
 
 	errno = 0;
-	spr = strtoull(argv[optind + 1], &endptr, 0);
+	gpr = strtoul(argv[optind + 1], &endptr, 0);
 	if (errno || *endptr != '\0') {
-		printf("%s: command '%s' couldn't parse GPR '%s'\n",
-				argv[0], argv[optind], argv[optind + 1]);
+		printf("%s: command '%s' couldn't parse SPR '%s'\n",
+		       argv[0], argv[optind], argv[optind + 1]);
 		return -1;
 	}
 
-	spr += REG_R31;
+	if (gpr > 0x3ff) {
+		printf("A SPR must be between zero and 1023 inclusive\n");
+		return -1;
+	}
 
-	if (strcmp(argv[optind], "putspr") == 0) {
-		uint64_t data;
+	return gpr;
+}
 
-		if (optind + 2 >= argc) {
-			printf("%s: command '%s' requires data\n", argv[0], argv[optind]);
-			return -1;
-		}
+int handle_getspr(int optind, int argc, char *argv[])
+{
+	uint64_t spr;
 
-		errno = 0;
-		data = strtoull(argv[optind + 2], &endptr, 0);
-		if (errno || *endptr != '\0') {
-			printf("%s: command '%s' couldn't parse data '%s'\n",
-				argv[0], argv[optind], argv[optind + 1]);
-			return -1;
-		}
+	if ((spr = parse_spr(optind, argc, argv)) < 0)
+		return -1;
 
-		return for_each_target("thread", putprocreg, &spr, &data);
-	}
+	spr += REG_R31;
 
 	return for_each_target("thread", getprocreg, &spr, NULL);
 }
 
-int handle_msr(int optind, int argc, char *argv[])
+int handle_putspr(int optind, int argc, char *argv[])
 {
-	uint64_t msr = REG_MSR;
-	char *endptr;
+	uint64_t spr, data;
 
-	if (strcmp(argv[optind], "putmsr") == 0) {
-		uint64_t data;
+	if ((spr = parse_spr(optind, argc, argv)) < 0)
+		return -1;
 
-		if (optind + 2 >= argc) {
-			printf("%s: command '%s' requires data\n", argv[0], argv[optind]);
-			return -1;
-		}
+	spr += REG_R31;
+	if (parse_data(optind, argc, argv, &data))
+		return -1;
 
-		errno = 0;
-		data = strtoull(argv[optind + 2], &endptr, 0);
-		if (errno || *endptr != '\0') {
-			printf("%s: command '%s' couldn't parse data '%s'\n",
-				argv[0], argv[optind], argv[optind + 1]);
-			return -1;
-		}
+	return for_each_target("thread", putprocreg, &spr, &data);
+}
 
-		return for_each_target("thread", putprocreg, &msr, &data);
-	}
+int handle_getmsr(int optind, int argc, char *argv[])
+{
+	uint64_t msr = REG_MSR;
 
 	return for_each_target("thread", getprocreg, &msr, NULL);
 }
+
+int handle_putmsr(int optind, int argc, char *argv[])
+{
+	uint64_t msr = REG_MSR, data;
+
+	if (parse_data(optind, argc, argv, &data))
+		return -1;
+
+	return for_each_target("thread", putprocreg, &msr, &data);
+}
diff --git a/src/reg.h b/src/reg.h
index ad41d9d..9ee2cd4 100644
--- a/src/reg.h
+++ b/src/reg.h
@@ -14,7 +14,11 @@
  * limitations under the License.
  */
 
-int handle_gpr(int optind, int argc, char *argv[]);
-int handle_nia(int optind, int argc, char *argv[]);
-int handle_spr(int optind, int argc, char *argv[]);
-int handle_msr(int optind, int argc, char *argv[]);
+int handle_getgpr(int optind, int argc, char *argv[]);
+int handle_putgpr(int optind, int argc, char *argv[]);
+int handle_getnia(int optind, int argc, char *argv[]);
+int handle_putnia(int optind, int argc, char *argv[]);
+int handle_getspr(int optind, int argc, char *argv[]);
+int handle_putspr(int optind, int argc, char *argv[]);
+int handle_getmsr(int optind, int argc, char *argv[]);
+int handle_putmsr(int optind, int argc, char *argv[]);
