diff --git a/src/validators/crypto_addresses/btc_address.py b/src/validators/crypto_addresses/btc_address.py
index f781f3b9..8eeb428c 100644
--- a/src/validators/crypto_addresses/btc_address.py
+++ b/src/validators/crypto_addresses/btc_address.py
@@ -48,9 +48,10 @@ def btc_address(value: str, /):
     if not value:
         return False
 
-    return (
-        # segwit pattern
-        re.compile(r"^(bc|tb)[0-3][02-9ac-hj-np-z]{14,74}$").fullmatch(value)
-        if value[:2] in ("bc", "tb")
-        else _validate_old_btc_address(value)
-    )
+    if value[:2].lower() in ("bc", "tb"):
+        # BIP 173 allows uniform upper/lowercase, but never mixed case.
+        if not value.isascii() or not (value.islower() or value.isupper()):
+            return False
+        return re.fullmatch(r"(bc|tb)[0-3][02-9ac-hj-np-z]{14,74}", value.lower())
+
+    return _validate_old_btc_address(value)
diff --git a/tests/crypto_addresses/test_btc_address.py b/tests/crypto_addresses/test_btc_address.py
index 96647eab..66603ef2 100644
--- a/tests/crypto_addresses/test_btc_address.py
+++ b/tests/crypto_addresses/test_btc_address.py
@@ -41,3 +41,48 @@ def test_returns_true_on_valid_btc_address(value: str):
 def test_returns_failed_validation_on_invalid_btc_address(value: str):
     """Test returns failed validation on invalid btc address."""
     assert isinstance(btc_address(value), ValidationError)
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        "bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4",
+        "tb1qw508d6qejxtdg4y5r3zarvary0c5xw7kxpjzsx",
+        "bc1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3qccfmv3",
+        "tb1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3q0sl5k7",
+    ],
+)
+def test_segwit_accepts_uniform_case(value: str):
+    """Accept lowercase and uppercase mainnet and testnet SegWit addresses."""
+    assert btc_address(value) is True
+    assert btc_address(value.upper()) is True
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        "BC1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4",
+        "bc1QW508D6QEJXTDG4Y5R3ZARVARY0C5XW7KV8F3T4",
+        "bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4".replace("q", "Q", 1),
+        "TB1qw508d6qejxtdg4y5r3zarvary0c5xw7kxpjzsx",
+        "tb1QW508D6QEJXTDG4Y5R3ZARVARY0C5XW7KXPJZSX",
+        "tb1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3q0sL5k7",
+    ],
+)
+def test_segwit_rejects_mixed_case(value: str):
+    """Do not accept a case change confined to the prefix or data part."""
+    assert isinstance(btc_address(value), ValidationError)
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        "bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4\n",
+        "BC1QW508D6QEJXTDG4Y5R3ZARVARY0C5XW7KV8F3T4\n",
+        "bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4".replace("k", "\u212a"),
+        "BC1QW508D6QEJXTDG4Y5R3ZARVARY0C5XW7KV8F3T4".replace("K", "\u212a"),
+    ],
+)
+def test_segwit_rejects_non_ascii_and_trailing_characters(value: str):
+    """Case normalization must not admit Unicode lookalikes or trailing text."""
+    assert isinstance(btc_address(value), ValidationError)