diff --git a/docs/environment.rst b/docs/environment.rst
index 2899a75aff8..6424df4627d 100644
--- a/docs/environment.rst
+++ b/docs/environment.rst
@@ -53,8 +53,11 @@ Details of the TOML language subset
 * The supported data types are strings, integers, floats, and booleans.
 * Whitespace is allowed.
 * Only basic strings are supported, not triple-quoted strings.
-* Only integers supported by ``strtol()`` can be parsed:
-  no ``0o``, no ``0b``, no underscores ``1_000``, ``011`` is 9, not 11.
+* Integers may be decimal, hexadecimal ``0x1F``, octal ``0o17``, or binary ``0b101``,
+  and may contain underscores ``1_000``.
+  Unlike TOML, a sign is also allowed before ``0x``, ``0o``, and ``0b``,
+  the prefix may be uppercase, and underscores need not be between digits.
+* Leading zeros are not allowed: ``011`` is an error, not 9 or 11.
 * Only bare keys are supported.
 * Duplicate keys are not diagnosed.
 * Comments are allowed.
diff --git a/shared-bindings/supervisor/__init__.c b/shared-bindings/supervisor/__init__.c
index a331249998a..eed98d21faa 100644
--- a/shared-bindings/supervisor/__init__.c
+++ b/shared-bindings/supervisor/__init__.c
@@ -379,11 +379,15 @@ MP_DEFINE_CONST_FUN_OBJ_KW(supervisor_set_usb_identification_obj, 0, supervisor_
 //|     - ``str``: Double-quoted string.
 //|       The string may include Unicode characters, and ``\\u`` Unicode escapes. Backslash-escaped characters
 //|       ``\\b``, ``\\r``, ``\\n``, ``\\t``, ``\\v``, ``\\v`` are also allowed.
-//|     - ``int``: signed or unsigned integer.
+//|     - ``int``: signed or unsigned integer: decimal, or hexadecimal ``0x1F``, octal ``0o17``,
+//|       or binary ``0b101``. Underscores are allowed: ``1_000``.
 //|     - ``bool``: lower-case ``true`` or ``false``.
 //|       The values are returned as Python ``True`` or ``False`` values.
 //|     - ``float``: signed or unsigned decimal number with a ``.`` or exponent, or ``inf``, ``inf``, ``nan``.
 //|
+//|     Leading zeros are not allowed in integers or in the integer part of floats:
+//|     ``017`` and ``01.5`` are errors.
+//|
 //|     Example::
 //|
 //|         # settings.toml:
diff --git a/supervisor/shared/settings.c b/supervisor/shared/settings.c
index fe13a4e6416..b658770f45f 100644
--- a/supervisor/shared/settings.c
+++ b/supervisor/shared/settings.c
@@ -185,16 +185,49 @@ static bool key_matches(file_arg *file_handle, const char *key) {
     return true;
 }
 
+// Parse digits in base 2 to 16, skipping any '_' after the first digit.
+// Used instead of strtol() and strtoul(), which would pull in about 0.8 kB of libc.
+//
+// Returns a pointer past the last digit, or NULL if there are no digits or the value
+// overflows mp_uint_t. *value is not touched on error.
+static const char *parse_digits(const char *str, mp_uint_t base, mp_uint_t *value) {
+    const char *start = str;
+    mp_uint_t val = 0;
+    for (;; str++) {
+        mp_uint_t dig = (unsigned char)*str;
+        if (dig == '_' && str != start) {
+            continue;
+        }
+        if ('0' <= dig && dig <= '9') {
+            dig -= '0';
+        } else if ((dig | 0x20) >= 'a') {
+            // Lowercase; anything past 'z' ends up >= base.
+            dig = (dig | 0x20) - 'a' + 10;
+        } else {
+            break;
+        }
+        if (dig >= base) {
+            break;
+        }
+        if (__builtin_mul_overflow(val, base, &val) || __builtin_add_overflow(val, dig, &val)) {
+            return NULL;
+        }
+    }
+    if (str == start) {
+        return NULL;
+    }
+    *value = val;
+    return str;
+}
+
 static settings_err_t read_unicode_escape(file_arg *file_handle, int sz, vstr_t *vstr) {
-    char hex_buf[sz + 1];
+    mp_uint_t c = 0;
     for (int i = 0; i < sz; i++) {
-        hex_buf[i] = get_next_byte(file_handle);
-    }
-    hex_buf[sz] = 0;
-    char *end;
-    unsigned long c = strtoul(hex_buf, &end, 16);
-    if (end != &hex_buf[sz]) {
-        return SETTINGS_ERR_BAD_VALUE;
+        uint8_t hex = get_next_byte(file_handle);
+        if (!unichar_isxdigit(hex)) {
+            return SETTINGS_ERR_BAD_VALUE;
+        }
+        c = c * 16 + unichar_xdigit_value(hex);
     }
     if (c >= 0x110000) {
         return SETTINGS_ERR_UNICODE;
@@ -403,15 +436,44 @@ static settings_err_t get_int(const char *key, mp_int_t *value) {
     if (quoted) {
         return SETTINGS_ERR_BAD_VALUE;
     }
-    char *end;
-    long num = strtol(buf, &end, 0);
-    while (unichar_isspace(*end)) {
-        end++;
+    // Accept a superset of TOML: a sign is also allowed before 0x, 0o and 0b, the prefix
+    // may be uppercase, and underscores need not be between digits.
+    const char *str = buf;
+    bool neg = false;
+    if (*str == '+' || *str == '-') {
+        neg = *str == '-';
+        str++;
+    }
+    mp_uint_t base = 10;
+    if (str[0] == '0') {
+        char prefix = str[1] | 0x20;
+        if (prefix == 'x') {
+            base = 16;
+        } else if (prefix == 'o') {
+            base = 8;
+        } else if (prefix == 'b') {
+            base = 2;
+        }
+        if (base != 10) {
+            str += 2;
+        } else if (unichar_isdigit(str[1])) {
+            // TOML does not allow leading zeros on decimal integers.
+            return SETTINGS_ERR_BAD_VALUE;
+        }
     }
-    if (end == buf || *end) { // If the whole buffer was not consumed it's an error
+    mp_uint_t magnitude;
+    str = parse_digits(str, base, &magnitude);
+    // A negative value can be one larger than MP_INT_MAX.
+    if (str == NULL || magnitude > (mp_uint_t)MP_INT_MAX + neg) {
         return SETTINGS_ERR_BAD_VALUE;
     }
-    *value = (mp_int_t)num;
+    while (unichar_isspace(*str)) {
+        str++;
+    }
+    if (*str) { // If the whole buffer was not consumed it's an error
+        return SETTINGS_ERR_BAD_VALUE;
+    }
+    *value = (mp_int_t)(neg ? 0 - magnitude : magnitude);
     return SETTINGS_OK;
 }
 
@@ -452,6 +514,15 @@ settings_err_t settings_get_bool(const char *key, bool *value) {
 }
 
 #if MICROPY_PY_BUILTINS_FLOAT
+// TOML does not allow leading zeros on decimal integers or on the integer part of floats.
+// https://toml.io/en/v1.0.0#integer and https://toml.io/en/v1.0.0#float
+static bool has_leading_zero(const char *str) {
+    if (*str == '+' || *str == '-') {
+        str++;
+    }
+    return str[0] == '0' && unichar_isdigit(str[1]);
+}
+
 static settings_err_t get_float(const char *key, mp_float_t *value) {
     char buf[48];
     bool quoted;
@@ -459,7 +530,7 @@ static settings_err_t get_float(const char *key, mp_float_t *value) {
     if (result != SETTINGS_OK) {
         return result;
     }
-    if (quoted) {
+    if (quoted || has_leading_zero(buf)) {
         return SETTINGS_ERR_BAD_VALUE;
     }
 
diff --git a/tests/circuitpython-manual/settings/code.py b/tests/circuitpython-manual/settings/code.py
index bebed3d11ae..f5e41abfc43 100644
--- a/tests/circuitpython-manual/settings/code.py
+++ b/tests/circuitpython-manual/settings/code.py
@@ -27,10 +27,18 @@ def check(key, expected):
 check("int_val", 42)
 check("neg_int_val", -7)
 check("hex_int_val", 31)
+check("hex_leading_zero_val", 15)  # TOML allows leading zeros after 0x
+check("neg_hex_int_val", -17)  # not TOML, but accepted
+check("oct_int_val", 15)
+check("bin_int_val", 17)
+check("underscore_int_val", 1000)  # used to fall back to float 1000.0
+check("zero_int_val", 0)
+check("signed_zero_val", 0)
 check("bool_true", True)
 check("bool_false", False)
 check("float_val", 3.14)
 check("neg_float_val", -1.5)
+check("frac_float_val", 0.5)
 check("sci_float_val", 6.626e-34)
 # math.nan and math.inf are not always available
 check("pos_inf", float("inf"))
@@ -50,6 +58,14 @@ def check_bad(key):
 check_bad("bad_float_junk")  # float with trailing garbage
 check_bad("bad_inf_junk")  # inf with trailing characters
 check_bad("bad_lone_sign")  # bare + with nothing after it
+check_bad("bad_leading_zero")  # TOML does not allow leading zeros
+check_bad("bad_leading_zero_neg")  # also after a sign
+check_bad("bad_leading_zero_08")  # not octal, so it used to fall back to float
+check_bad("bad_leading_zero_float")  # nor on the integer part of a float
+check_bad("bad_hex_no_digits")  # prefix with no digits
+check_bad("bad_hex_overflow")  # does not fit in a 32-bit int
+check_bad("bad_digit_at")  # '@' is not a digit
+check_bad("bad_unicode_underscore")  # no underscores in \u escapes
 
 # Missing key returns default
 got = supervisor.get_setting("no_such_key", "default")
diff --git a/tests/circuitpython-manual/settings/settings.toml b/tests/circuitpython-manual/settings/settings.toml
index 5df2d104afe..d52b70eb1df 100644
--- a/tests/circuitpython-manual/settings/settings.toml
+++ b/tests/circuitpython-manual/settings/settings.toml
@@ -3,13 +3,29 @@ bad_word = hello
 bad_float_junk = 1.2abc
 bad_inf_junk = infoo
 bad_lone_sign = +
+bad_leading_zero = 017
+bad_leading_zero_neg = -017
+bad_leading_zero_08 = 08
+bad_leading_zero_float = 01.5
+bad_hex_no_digits = 0x
+bad_hex_overflow = 0x1_0000_0000
+bad_digit_at = 12@
+bad_unicode_underscore = "\u0_41"
 int_val = 42
 neg_int_val = -7
 hex_int_val = 0x1F
+hex_leading_zero_val = 0x000F
+neg_hex_int_val = -0x11
+oct_int_val = 0o17
+bin_int_val = 0b10001
+underscore_int_val = 1_000
+zero_int_val = 0
+signed_zero_val = -0
 bool_true = true
 bool_false = false
 float_val = 3.14
 neg_float_val = -1.5
+frac_float_val = 0.5
 sci_float_val = 6.626e-34
 pos_inf = inf
 neg_inf = -inf