diff --git a/python_multipart/multipart.py b/python_multipart/multipart.py
index 49cdd8e..ed990c7 100644
--- a/python_multipart/multipart.py
+++ b/python_multipart/multipart.py
@@ -714,7 +714,7 @@ def __init__(self, callbacks: OctetStreamCallbacks = {}, max_size: float = float
         self.callbacks = callbacks
         self._started = False
 
-        if not isinstance(max_size, Number) or max_size < 1:
+        if isinstance(max_size, bool) or not isinstance(max_size, Number) or max_size < 1:
             raise ValueError("max_size must be a positive number, not %r" % max_size)
         self.max_size: int | float = max_size
         self._current_size = 0
@@ -796,7 +796,7 @@ def __init__(
         self.callbacks = callbacks
 
         # Max-size stuff
-        if not isinstance(max_size, Number) or max_size < 1:
+        if isinstance(max_size, bool) or not isinstance(max_size, Number) or max_size < 1:
             raise ValueError("max_size must be a positive number, not %r" % max_size)
         self.max_size: int | float = max_size
         self._current_size = 0
@@ -1049,11 +1049,20 @@ def __init__(
 
         self.callbacks = callbacks
 
-        if not isinstance(max_size, Number) or max_size < 1:
+        if isinstance(max_size, bool) or not isinstance(max_size, Number) or max_size < 1:
             raise ValueError("max_size must be a positive number, not %r" % max_size)
         self.max_size = max_size
         self._current_size = 0
 
+        # bool subclasses int; True would silently become count/size 1
+        if isinstance(max_header_count, bool) or not isinstance(max_header_count, int):
+            raise ValueError(
+                "max_header_count must be an int, not %r" % max_header_count
+            )
+        if isinstance(max_header_size, bool) or not isinstance(max_header_size, int):
+            raise ValueError(
+                "max_header_size must be an int, not %r" % max_header_size
+            )
         self.max_header_count = max_header_count
         self._current_header_count = 0
 
diff --git a/tests/test_multipart.py b/tests/test_multipart.py
index 949d70c..8d665c5 100644
--- a/tests/test_multipart.py
+++ b/tests/test_multipart.py
@@ -512,6 +512,12 @@ def test_invalid_max_size(self) -> None:
         with self.assertRaises(ValueError):
             p = QuerystringParser(max_size=-100)
 
+    def test_rejects_bool_max_size(self) -> None:
+        """bool is a Number; max_size=True must not silently become 1."""
+        for value in (True, False):
+            with self.assertRaises(ValueError):
+                QuerystringParser(max_size=value)
+
     def test_strict_parsing_pass(self) -> None:
         data = b"foo=bar&another=asdf"
         for first, last in split_all(data):
@@ -639,6 +645,12 @@ def test_invalid_max_size(self) -> None:
         with self.assertRaises(ValueError):
             q = OctetStreamParser(max_size="foo")  # type: ignore[arg-type]
 
+    def test_rejects_bool_max_size_octet(self) -> None:
+        """bool is a Number; max_size=True must not silently become 1."""
+        for value in (True, False):
+            with self.assertRaises(ValueError):
+                OctetStreamParser(max_size=value)
+
 
 class TestBase64Decoder(unittest.TestCase):
     # Note: base64('foobar') == 'Zm9vYmFy'
@@ -1592,6 +1604,21 @@ def test_invalid_max_size_multipart(self) -> None:
         with self.assertRaises(ValueError):
             MultipartParser(b"bound", max_size="foo")  # type: ignore[arg-type]
 
+    def test_rejects_bool_max_size_and_header_limits(self) -> None:
+        """bool subclasses Number/int; True must not silently become size/count 1."""
+        for value in (True, False):
+            with self.assertRaises(ValueError):
+                MultipartParser(b"bound", max_size=value)
+            with self.assertRaises(ValueError):
+                MultipartParser(b"bound", max_header_count=value)
+            with self.assertRaises(ValueError):
+                MultipartParser(b"bound", max_header_size=value)
+        # valid ints still accepted
+        p = MultipartParser(b"bound", max_size=100, max_header_count=4, max_header_size=256)
+        assert p.max_size == 100
+        assert p.max_header_count == 4
+        assert p.max_header_size == 256
+
     def test_boundary_too_long(self) -> None:
         with self.assertRaisesRegex(FormParserError, "Boundary length 257 exceeds maximum of 256"):
             MultipartParser(b"x" * 257)