diff --git a/setup.cfg b/setup.cfg
index 8c93574..f5ddb8c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -32,7 +32,10 @@ package_dir =
 packages = find:
 python_requires = >=3.9
 install_requires =
-    typeguard>=4
+    # typeguard 4.3.0 breaks "intersection" protocols, see linked issue. I didn't figure
+    # out a way to work around this at the moment, so it needs to be pinned.
+    # https://github.com/antonagestam/phantom-types/issues/299
+    typeguard>=4,<4.3.0
     typing_extensions>=4.3.0
     numerary>=0.4.3
 
diff --git a/src/phantom/ext/phonenumbers.py b/src/phantom/ext/phonenumbers.py
index de792fd..23444aa 100644
--- a/src/phantom/ext/phonenumbers.py
+++ b/src/phantom/ext/phonenumbers.py
@@ -13,6 +13,7 @@
 from typing import cast
 
 import phonenumbers
+from typing_extensions import TypeGuard
 
 from phantom import Phantom
 from phantom.bounds import parse_str
@@ -67,7 +68,7 @@ def normalize_phone_number(
 is_phone_number = excepts(InvalidPhoneNumber)(_deconstruct_phone_number)
 
 
-def is_formatted_phone_number(number: str) -> bool:
+def is_formatted_phone_number(number: str) -> TypeGuard[FormattedPhoneNumber]:
     try:
         return number == normalize_phone_number(number)
     except InvalidPhoneNumber:
diff --git a/tests/ext/test_phonenumbers.py b/tests/ext/test_phonenumbers.py
index 9602559..e265866 100644
--- a/tests/ext/test_phonenumbers.py
+++ b/tests/ext/test_phonenumbers.py
@@ -1,4 +1,5 @@
 import pytest
+from typing_extensions import assert_type
 
 from phantom.errors import BoundError
 from phantom.ext.phonenumbers import FormattedPhoneNumber
@@ -103,8 +104,10 @@ def test_returns_false_for_invalid_number(self):
 
 
 class TestIsFormattedPhoneNumber:
-    def test_returns_true_for_formatted_number(self):
-        assert is_formatted_phone_number("+46123456789") is True
+    def test_returns_true_for_formatted_number(self) -> None:
+        value = "+46123456789"
+        assert is_formatted_phone_number(value)
+        assert_type(value, FormattedPhoneNumber)
 
     def test_returns_false_for_unformatted_number(self):
         assert is_formatted_phone_number("+46 (123) 456 789") is False