diff --git a/schema/__init__.py b/schema/__init__.py
index 10d6e8a..6533090 100644
--- a/schema/__init__.py
+++ b/schema/__init__.py
@@ -246,7 +246,7 @@ def __init__(
     ) -> None:
         self._pattern_str: str = pattern_str
         flags_list = [
-            Regex.NAMES[i] for i, f in enumerate(f"{flags:09b}") if f != "0"
+            Regex.NAMES[i] for i, f in enumerate(f"{int(flags):09b}") if f != "0"
         ]  # Name for each bit
 
         self._flags_names: str = ", flags=" + "|".join(flags_list) if flags_list else ""
diff --git a/test_schema.py b/test_schema.py
index 4d78456..adaf216 100644
--- a/test_schema.py
+++ b/test_schema.py
@@ -215,6 +215,19 @@ def test_regex():
         Regex(None).validate("bar")
 
 
+def test_regex_flags():
+    # Passing an actual re flag (a re.RegexFlag enum member, not a plain int)
+    # must not crash while building the human-readable repr, and the flag must
+    # still be applied. On CPython <= 3.10 and PyPy, formatting a RegexFlag with
+    # the "b" format code raised ValueError before the flag was compiled.
+    single = Regex(r"foo", flags=re.IGNORECASE)
+    assert single.validate("FOObar") == "FOObar"
+    assert "re.IGNORECASE" in repr(single)
+
+    multi = Regex(r"^foo", flags=re.IGNORECASE | re.MULTILINE)
+    assert multi.validate("bar\nFOO") == "bar\nFOO"
+
+
 def test_validate_list():
     assert Schema([1, 0]).validate([1, 0, 1, 1]) == [1, 0, 1, 1]
     assert Schema([1, 0]).validate([]) == []