diff --git a/bootstrap/helpers/github.php b/bootstrap/helpers/github.php
index 69991f52e..acb93c93a 100644
--- a/bootstrap/helpers/github.php
+++ b/bootstrap/helpers/github.php
@@ -38,22 +38,23 @@ function githubUrlHost(?string $url): ?string
 /**
  * Build the scheme://host[:port] origin for a GitHub URL.
  *
- * When the host cannot be parsed (e.g. a scheme-less or malformed URL such as
- * "not-a-url"), the input is returned verbatim with any trailing slashes
- * trimmed. Callers should pass already-validated URLs (see SafeExternalUrl),
- * so this fallback only guards against unexpected input.
+ * This helper fails explicitly for blank, scheme-less, or malformed input when
+ * githubUrlHost() cannot parse a host, because returning the original input
+ * would not be a valid origin. Callers should pass already-validated URLs.
  *
  * @param  string  $url  The URL to derive the origin from
- * @return string The normalized origin, or the trimmed input when the host is unparseable
+ * @return string The normalized origin
+ *
+ * @throws InvalidArgumentException When the URL does not contain a parseable scheme and host
  */
 function githubUrlOrigin(string $url): string
 {
-    $scheme = parse_url($url, PHP_URL_SCHEME) ?: 'https';
+    $scheme = parse_url($url, PHP_URL_SCHEME);
     $host = githubUrlHost($url);
     $port = parse_url($url, PHP_URL_PORT);
 
-    if (! $host) {
-        return rtrim($url, '/');
+    if (! is_string($scheme) || blank($scheme) || ! $host) {
+        throw new InvalidArgumentException('GitHub URL must include a valid scheme and host.');
     }
 
     return $scheme.'://'.$host.($port ? ":{$port}" : '');
diff --git a/tests/Feature/Api/GithubAppsListApiTest.php b/tests/Feature/Api/GithubAppsListApiTest.php
index 6357c25ba..8f3e6dac5 100644
--- a/tests/Feature/Api/GithubAppsListApiTest.php
+++ b/tests/Feature/Api/GithubAppsListApiTest.php
@@ -322,6 +322,32 @@ function validGithubAppsApiPrivateKey(): string
             ->assertJsonPath('data.api_url', 'https://github.com/api/v3');
     });
 
+    test('preserves provided api url when updating api url only', function () {
+        $githubApp = GithubApp::create([
+            'name' => 'GHE App',
+            'api_url' => 'https://api.github.com',
+            'html_url' => 'https://github.com',
+            'app_id' => 12345,
+            'installation_id' => 67890,
+            'client_id' => 'test-client-id',
+            'client_secret' => 'test-client-secret',
+            'webhook_secret' => 'test-webhook-secret',
+            'private_key_id' => $this->privateKey->id,
+            'team_id' => $this->team->id,
+            'is_system_wide' => false,
+            'is_public' => false,
+        ]);
+
+        $response = $this->withHeaders([
+            'Authorization' => 'Bearer '.$this->bearerToken,
+        ])->patchJson("/api/v1/github-apps/{$githubApp->id}", [
+            'api_url' => 'https://github.com/api/v3',
+        ]);
+
+        $response->assertSuccessful()
+            ->assertJsonPath('data.api_url', 'https://github.com/api/v3');
+    });
+
     test('rejects invalid organization when creating github apps', function () {
         $response = $this->withHeaders([
             'Authorization' => 'Bearer '.$this->bearerToken,
diff --git a/tests/Unit/GithubUrlHelpersTest.php b/tests/Unit/GithubUrlHelpersTest.php
index 7c4ee6ff5..dcace7ebe 100644
--- a/tests/Unit/GithubUrlHelpersTest.php
+++ b/tests/Unit/GithubUrlHelpersTest.php
@@ -23,6 +23,14 @@
     'github enterprise server' => ['https://github.company.internal', 'https://github.company.internal/api/v3'],
 ]);
 
+it('rejects malformed urls when deriving an origin', function (string $url) {
+    expect(fn () => githubUrlOrigin($url))->toThrow(InvalidArgumentException::class);
+})->with([
+    'blank' => [''],
+    'scheme-less' => ['github.company.internal'],
+    'malformed' => ['not-a-url'],
+]);
+
 it('generates correct install paths for github cloud ghe cloud and ghes', function (array $attributes, string $expectedPrefix) {
     $githubApp = new GithubApp;
     $githubApp->forceFill(array_merge([