diff --git a/gdbstub.c b/gdbstub.c
index f936ddd32d..2a94030d3b 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -911,7 +911,7 @@ static int gdb_handle_vcont(GDBState *s, const char *p)
 
         cur_action = *p++;
         if (cur_action == 'C' || cur_action == 'S') {
-            cur_action = tolower(cur_action);
+            cur_action = qemu_tolower(cur_action);
             res = qemu_strtoul(p + 1, &p, 16, &tmp);
             if (res) {
                 goto out;
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index ce3921e4de..1c7af39ce6 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -318,7 +318,7 @@ static void machine_set_loadparm(Object *obj, const char *val, Error **errp)
     int i;
 
     for (i = 0; i < sizeof(ms->loadparm) && val[i]; i++) {
-        uint8_t c = toupper(val[i]); /* mimic HMC */
+        uint8_t c = qemu_toupper(val[i]); /* mimic HMC */
 
         if (('A' <= c && c <= 'Z') || ('0' <= c && c <= '9') || (c == '.') ||
             (c == ' ')) {
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index a55ff87c22..7e1cbab77e 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -406,7 +406,7 @@ static int read_naa_id(const uint8_t *p, uint64_t *p_wwn)
         }
         *p_wwn = 0;
         for (i = 8; i < 24; i++) {
-            char c = toupper(p[i]);
+            char c = qemu_toupper(p[i]);
             c -= (c >= '0' && c <= '9' ? '0' : 'A' - 10);
             *p_wwn = (*p_wwn << 4) | c;
         }
diff --git a/target/ppc/monitor.c b/target/ppc/monitor.c
index b8f30e9eaf..14915119fc 100644
--- a/target/ppc/monitor.c
+++ b/target/ppc/monitor.c
@@ -115,14 +115,14 @@ int target_get_monitor_def(CPUState *cs, const char *name, uint64_t *pval)
     CPUPPCState *env = &cpu->env;
 
     /* General purpose registers */
-    if ((tolower(name[0]) == 'r') &&
+    if ((qemu_tolower(name[0]) == 'r') &&
         ppc_cpu_get_reg_num(name + 1, ARRAY_SIZE(env->gpr), &regnum)) {
         *pval = env->gpr[regnum];
         return 0;
     }
 
     /* Floating point registers */
-    if ((tolower(name[0]) == 'f') &&
+    if ((qemu_tolower(name[0]) == 'f') &&
         ppc_cpu_get_reg_num(name + 1, ARRAY_SIZE(env->fpr), &regnum)) {
         *pval = env->fpr[regnum];
         return 0;