diff --git a/src/snowflake/connector/connection.py b/src/snowflake/connector/connection.py
index 6b46249451..a89a8e2d5c 100644
--- a/src/snowflake/connector/connection.py
+++ b/src/snowflake/connector/connection.py
@@ -134,7 +134,12 @@
 from .telemetry import TelemetryClient, TelemetryData, TelemetryField
 from .time_util import HeartBeatTimer, get_time_millis
 from .url_util import extract_top_level_domain_from_hostname
-from .util_text import construct_hostname, parse_account, split_statements
+from .util_text import (
+    construct_hostname,
+    is_valid_account_identifier,
+    parse_account,
+    split_statements,
+)
 from .wif_util import AttestationProvider
 
 if sys.version_info >= (3, 13) or typing.TYPE_CHECKING:
@@ -1743,8 +1748,20 @@ def __config(self, **kwargs):
                 ProgrammingError,
                 {"msg": "Account must be specified", "errno": ER_NO_ACCOUNT_NAME},
             )
-        if self._account and "." in self._account:
-            self._account = parse_account(self._account)
+        if self._account:
+            # Allow legacy formats like "acc.region" to continue parsing into simple account id
+            if "." in self._account:
+                self._account = parse_account(self._account)
+            if not is_valid_account_identifier(self._account):
+                Error.errorhandler_wrapper(
+                    self,
+                    None,
+                    ProgrammingError,
+                    {
+                        "msg": "Invalid account identifier: only letters, digits, '_' and '-' allowed; no dots or slashes",
+                        "errno": ER_INVALID_VALUE,
+                    },
+                )
 
         if not isinstance(self._backoff_policy, Callable) or not isinstance(
             self._backoff_policy(), Iterator
diff --git a/src/snowflake/connector/util_text.py b/src/snowflake/connector/util_text.py
index 39762c2111..156f930bef 100644
--- a/src/snowflake/connector/util_text.py
+++ b/src/snowflake/connector/util_text.py
@@ -254,6 +254,22 @@ def _is_china_region(r: str) -> bool:
     return host
 
 
+ACCOUNT_ID_VALIDATOR_RE = re.compile(r"^[A-Za-z0-9_-]+$")
+
+
+def is_valid_account_identifier(account: str) -> bool:
+    """Validate the Snowflake account identifier format.
+
+    The account identifier must be a single label (no dots or slashes) composed
+    only of ASCII letters, digits, underscores, or hyphens.
+    """
+    if not isinstance(account, str) or not account:
+        return False
+    if "." in account or "/" in account or "\\" in account:
+        return False
+    return bool(ACCOUNT_ID_VALIDATOR_RE.fullmatch(account))
+
+
 def parse_account(account):
     url_parts = account.split(".")
     # if this condition is true, then we have some extra
diff --git a/test/unit/test_parse_account.py b/test/unit/test_parse_account.py
index c07dd46c05..e3ef04f4f1 100644
--- a/test/unit/test_parse_account.py
+++ b/test/unit/test_parse_account.py
@@ -1,7 +1,9 @@
 #!/usr/bin/env python
 from __future__ import annotations
 
-from snowflake.connector.util_text import parse_account
+import pytest
+
+from snowflake.connector.util_text import is_valid_account_identifier, parse_account
 
 
 def test_parse_account_basic():
@@ -12,3 +14,20 @@ def test_parse_account_basic():
     assert (
         parse_account("account1-jkabfvdjisoa778wqfgeruishafeuw89q.global") == "account1"
     )
+
+
+@pytest.mark.parametrize(
+    "value,expected",
+    [
+        ("abc", True),
+        ("ABC", True),
+        ("a_b-c1", True),
+        ("a.b", False),
+        ("a/b", False),
+        ("a\\b", False),
+        ("", False),
+        ("snowflakecomputing.com", False),
+    ],
+)
+def test_is_valid_account_identifier(value, expected):
+    assert is_valid_account_identifier(value) is expected