diff --git a/app/core/validation.py b/app/core/validation.py
index e219a95..5994cc0 100644
--- a/app/core/validation.py
+++ b/app/core/validation.py
@@ -61,6 +61,11 @@ def validate_webhook_url(url: str) -> str:
     if parsed.username or parsed.password:
         raise UnsafeWebhookURLError("Webhook URL must not contain embedded credentials")
 
+    try:
+        port = parsed.port
+    except ValueError as exc:
+        raise UnsafeWebhookURLError("Webhook URL contains an invalid port") from exc
+
     settings = get_settings()
     if settings.allow_private_webhooks:
         return url
@@ -68,7 +73,11 @@ def validate_webhook_url(url: str) -> str:
     try:
         addresses = {
             item[4][0]
-            for item in socket.getaddrinfo(parsed.hostname, parsed.port or 443, type=socket.SOCK_STREAM)
+            for item in socket.getaddrinfo(
+                parsed.hostname,
+                port or (443 if parsed.scheme == "https" else 80),
+                type=socket.SOCK_STREAM,
+            )
         }
     except socket.gaierror as exc:
         raise UnsafeWebhookURLError("Webhook hostname could not be resolved") from exc
diff --git a/tests/test_validation.py b/tests/test_validation.py
index 18098f4..71ee855 100644
--- a/tests/test_validation.py
+++ b/tests/test_validation.py
@@ -3,7 +3,13 @@
 
 import pytest
 
-from core.validation import sanitize_filename_prefix, validate_batch_pages
+import core.validation as validation
+from core.validation import (
+    UnsafeWebhookURLError,
+    sanitize_filename_prefix,
+    validate_batch_pages,
+    validate_webhook_url,
+)
 
 
 def test_filename_prefix_rejects_path_traversal():
@@ -31,3 +37,45 @@ def test_batch_limits_page_count_and_size(monkeypatch):
     with pytest.raises(ValueError, match="single page"):
         validate_batch_pages(["A" * (2 * 1024 * 1024)])
     get_settings.cache_clear()
+
+
+@pytest.mark.parametrize(
+    "url",
+    ["https://example.com:not-a-port/hook", "https://example.com:70000/hook"],
+)
+def test_webhook_rejects_invalid_port_before_dns_lookup(monkeypatch, url):
+    monkeypatch.setattr(
+        validation,
+        "get_settings",
+        lambda: type("Settings", (), {"allow_private_webhooks": False})(),
+    )
+    monkeypatch.setattr(
+        validation.socket,
+        "getaddrinfo",
+        lambda *_args, **_kwargs: pytest.fail("DNS lookup must not run for an invalid port"),
+    )
+
+    with pytest.raises(UnsafeWebhookURLError, match="invalid port"):
+        validate_webhook_url(url)
+
+
+@pytest.mark.parametrize(
+    ("url", "expected_port"),
+    [("http://example.com/hook", 80), ("https://example.com/hook", 443)],
+)
+def test_webhook_uses_scheme_specific_default_port(monkeypatch, url, expected_port):
+    requested_ports = []
+    monkeypatch.setattr(
+        validation,
+        "get_settings",
+        lambda: type("Settings", (), {"allow_private_webhooks": False})(),
+    )
+
+    def resolve(_host, port, **_kwargs):
+        requested_ports.append(port)
+        return [(None, None, None, None, ("93.184.216.34", port))]
+
+    monkeypatch.setattr(validation.socket, "getaddrinfo", resolve)
+
+    assert validate_webhook_url(url) == url
+    assert requested_ports == [expected_port]