diff --git a/hmp.c b/hmp.c
index 72a5256676..2269e8b457 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1346,7 +1346,6 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
     const char *valuestr = qdict_get_str(qdict, "value");
     int64_t valuebw = 0;
     long valueint = 0;
-    char *endp;
     Error *err = NULL;
     bool use_int_value = false;
     int i;
@@ -1385,9 +1384,8 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
                 break;
             case MIGRATION_PARAMETER_MAX_BANDWIDTH:
                 p.has_max_bandwidth = true;
-                valuebw = qemu_strtosz_MiB(valuestr, &endp);
-                if (valuebw < 0 || (size_t)valuebw != valuebw
-                    || *endp != '\0') {
+                valuebw = qemu_strtosz_MiB(valuestr, NULL);
+                if (valuebw < 0 || (size_t)valuebw != valuebw) {
                     error_setg(&err, "Invalid size %s", valuestr);
                     goto cleanup;
                 }
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index b3d9ed99dd..848bebc794 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -1267,10 +1267,8 @@ static void ivshmem_realize(PCIDevice *dev, Error **errp)
     if (s->sizearg == NULL) {
         s->legacy_size = 4 << 20; /* 4 MB default */
     } else {
-        char *end;
-        int64_t size = qemu_strtosz_MiB(s->sizearg, &end);
-        if (size < 0 || (size_t)size != size || *end != '\0'
-            || !is_power_of_2(size)) {
+        int64_t size = qemu_strtosz_MiB(s->sizearg, NULL);
+        if (size < 0 || (size_t)size != size || !is_power_of_2(size)) {
             error_setg(errp, "Invalid size %s", s->sizearg);
             return;
         }
diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index 360d33773f..911a0ee300 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -482,15 +482,14 @@ opts_type_size(Visitor *v, const char *name, uint64_t *obj, Error **errp)
     OptsVisitor *ov = to_ov(v);
     const QemuOpt *opt;
     int64_t val;
-    char *endptr;
 
     opt = lookup_scalar(ov, name, errp);
     if (!opt) {
         return;
     }
 
-    val = qemu_strtosz(opt->str ? opt->str : "", &endptr);
-    if (val < 0 || *endptr) {
+    val = qemu_strtosz(opt->str ? opt->str : "", NULL);
+    if (val < 0) {
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE, opt->name,
                    "a size value representible as a non-negative int64");
         return;
diff --git a/qemu-img.c b/qemu-img.c
index 4062917603..39ef581cc1 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -370,14 +370,9 @@ static int add_old_style_options(const char *fmt, QemuOpts *opts,
 
 static int64_t cvtnum(const char *s)
 {
-    char *end;
     int64_t ret;
 
-    ret = qemu_strtosz(s, &end);
-    if (*end != '\0') {
-        /* Detritus at the end of the string */
-        return -EINVAL;
-    }
+    ret = qemu_strtosz(s, NULL);
     return ret;
 }
 
diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 0166cfaa8d..973eb94774 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -137,14 +137,9 @@ static char **breakline(char *input, int *count)
 
 static int64_t cvtnum(const char *s)
 {
-    char *end;
     int64_t ret;
 
-    ret = qemu_strtosz(s, &end);
-    if (*end != '\0') {
-        /* Detritus at the end of the string */
-        return -EINVAL;
-    }
+    ret = qemu_strtosz(s, NULL);
     return ret;
 }
 
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 685ca36640..58a05ec870 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -2034,10 +2034,9 @@ static void x86_cpu_parse_featurestr(const char *typename, char *features,
         /* Special case: */
         if (!strcmp(name, "tsc-freq")) {
             int64_t tsc_freq;
-            char *err;
 
-            tsc_freq = qemu_strtosz_metric(val, &err);
-            if (tsc_freq < 0 || *err) {
+            tsc_freq = qemu_strtosz_metric(val, NULL);
+            if (tsc_freq < 0) {
                 error_setg(errp, "bad numerical value %s", val);
                 return;
             }
diff --git a/tests/test-cutils.c b/tests/test-cutils.c
index c4437d9817..f2ecb7aecb 100644
--- a/tests/test-cutils.c
+++ b/tests/test-cutils.c
@@ -1510,10 +1510,16 @@ static void test_qemu_strtosz_trailing(void)
     g_assert_cmpint(res, ==, 123 * M_BYTE);
     g_assert(endptr == str + 3);
 
+    res = qemu_strtosz(str, NULL);
+    g_assert_cmpint(res, ==, -EINVAL);
+
     str = "1kiB";
     res = qemu_strtosz(str, &endptr);
     g_assert_cmpint(res, ==, 1024);
     g_assert(endptr == str + 2);
+
+    res = qemu_strtosz(str, NULL);
+    g_assert_cmpint(res, ==, -EINVAL);
 }
 
 static void test_qemu_strtosz_erange(void)
diff --git a/util/cutils.c b/util/cutils.c
index 0ac8019ef6..b991623733 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -208,7 +208,7 @@ static int64_t suffix_mul(char suffix, int64_t unit)
 static int64_t do_strtosz(const char *nptr, char **end,
                           const char default_suffix, int64_t unit)
 {
-    int64_t retval = -EINVAL;
+    int64_t retval;
     char *endptr;
     unsigned char c;
     int mul_required = 0;
@@ -217,7 +217,8 @@ static int64_t do_strtosz(const char *nptr, char **end,
     errno = 0;
     val = strtod(nptr, &endptr);
     if (isnan(val) || endptr == nptr || errno != 0) {
-        goto fail;
+        retval = -EINVAL;
+        goto out;
     }
     fraction = modf(val, &integral);
     if (fraction != 0) {
@@ -232,17 +233,20 @@ static int64_t do_strtosz(const char *nptr, char **end,
         assert(mul >= 0);
     }
     if (mul == 1 && mul_required) {
-        goto fail;
+        retval = -EINVAL;
+        goto out;
     }
     if ((val * mul >= INT64_MAX) || val < 0) {
         retval = -ERANGE;
-        goto fail;
+        goto out;
     }
     retval = val * mul;
 
-fail:
+out:
     if (end) {
         *end = endptr;
+    } else if (*endptr) {
+        retval = -EINVAL;
     }
 
     return retval;