diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 34b12a3..32cdd66 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -228,6 +228,20 @@ static void rtas_stop_self(PowerPCCPU *cpu, sPAPRMachineState *spapr,
     env->msr = 0;
 }
 
+
+static inline int sysparm_st(target_ulong addr, target_ulong len,
+                             const void *val, uint16_t vallen)
+{
+    hwaddr phys = ppc64_phys_to_real(addr);
+
+    if (len < 2) {
+        return RTAS_OUT_SYSPARM_PARAM_ERROR;
+    }
+    stw_be_phys(&address_space_memory, phys, vallen);
+    cpu_physical_memory_write(phys + 2, val, MIN(len - 2, vallen));
+    return RTAS_OUT_SUCCESS;
+}
+
 static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           sPAPRMachineState *spapr,
                                           uint32_t token, uint32_t nargs,
@@ -237,7 +251,7 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
     target_ulong parameter = rtas_ld(args, 0);
     target_ulong buffer = rtas_ld(args, 1);
     target_ulong length = rtas_ld(args, 2);
-    target_ulong ret = RTAS_OUT_SUCCESS;
+    target_ulong ret;
 
     switch (parameter) {
     case RTAS_SYSPARM_SPLPAR_CHARACTERISTICS: {
@@ -249,18 +263,18 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           current_machine->ram_size / M_BYTE,
                                           smp_cpus,
                                           max_cpus);
-        rtas_st_buffer(buffer, length, (uint8_t *)param_val, strlen(param_val));
+        ret = sysparm_st(buffer, length, param_val, strlen(param_val) + 1);
         g_free(param_val);
         break;
     }
     case RTAS_SYSPARM_DIAGNOSTICS_RUN_MODE: {
         uint8_t param_val = DIAGNOSTICS_RUN_MODE_DISABLED;
 
-        rtas_st_buffer(buffer, length, &param_val, sizeof(param_val));
+        ret = sysparm_st(buffer, length, &param_val, sizeof(param_val));
         break;
     }
     case RTAS_SYSPARM_UUID:
-        rtas_st_buffer(buffer, length, qemu_uuid, (qemu_uuid_set ? 16 : 0));
+        ret = sysparm_st(buffer, length, qemu_uuid, (qemu_uuid_set ? 16 : 0));
         break;
     default:
         ret = RTAS_OUT_NOT_SUPPORTED;
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index 53af76a..1e10fc9 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -408,14 +408,15 @@ int spapr_allocate_irq_block(int num, bool lsi, bool msi);
 #define RTAS_SLOT_PERM_ERR_LOG           2
 
 /* RTAS return codes */
-#define RTAS_OUT_SUCCESS            0
-#define RTAS_OUT_NO_ERRORS_FOUND    1
-#define RTAS_OUT_HW_ERROR           -1
-#define RTAS_OUT_BUSY               -2
-#define RTAS_OUT_PARAM_ERROR        -3
-#define RTAS_OUT_NOT_SUPPORTED      -3
-#define RTAS_OUT_NO_SUCH_INDICATOR  -3
-#define RTAS_OUT_NOT_AUTHORIZED     -9002
+#define RTAS_OUT_SUCCESS                        0
+#define RTAS_OUT_NO_ERRORS_FOUND                1
+#define RTAS_OUT_HW_ERROR                       -1
+#define RTAS_OUT_BUSY                           -2
+#define RTAS_OUT_PARAM_ERROR                    -3
+#define RTAS_OUT_NOT_SUPPORTED                  -3
+#define RTAS_OUT_NO_SUCH_INDICATOR              -3
+#define RTAS_OUT_NOT_AUTHORIZED                 -9002
+#define RTAS_OUT_SYSPARM_PARAM_ERROR            -9999
 
 /* RTAS tokens */
 #define RTAS_TOKEN_BASE      0x2000
@@ -513,17 +514,6 @@ static inline void rtas_st_buffer_direct(target_ulong phys,
                               MIN(buffer_len, phys_len));
 }
 
-static inline void rtas_st_buffer(target_ulong phys, target_ulong phys_len,
-                                  uint8_t *buffer, uint16_t buffer_len)
-{
-    if (phys_len < 2) {
-        return;
-    }
-    stw_be_phys(&address_space_memory,
-                ppc64_phys_to_real(phys), buffer_len);
-    rtas_st_buffer_direct(phys + 2, phys_len - 2, buffer, buffer_len);
-}
-
 typedef void (*spapr_rtas_fn)(PowerPCCPU *cpu, sPAPRMachineState *sm,
                               uint32_t token,
                               uint32_t nargs, target_ulong args,
