diff --git a/.ai/lessons.md b/.ai/lessons.md
index b4d51f943..89dce29f4 100644
--- a/.ai/lessons.md
+++ b/.ai/lessons.md
@@ -9,3 +9,6 @@ ## Alpine x-transition + tw-animate-css exit animations flash at the end
 ## Displayed defaults must not become stored overrides
 - When an edit form shows an inherited or computed default, trace an unchanged save and a related-field edit through persistence.
 - Preserve the inherited state when the displayed value still equals the computed default; store an override only when the user selects a different value.
+
+## Prove regressions against the unchanged baseline
+- For a bug fix, run the same regression test before and after the production change. Use a stash when requested so the failure and success come from the exact same test.
diff --git a/app/Jobs/ApplicationDeploymentJob.php b/app/Jobs/ApplicationDeploymentJob.php
index f260e619a..6d42398c2 100644
--- a/app/Jobs/ApplicationDeploymentJob.php
+++ b/app/Jobs/ApplicationDeploymentJob.php
@@ -2403,15 +2403,20 @@ private function set_coolify_variables()
             $fqdn = $this->preview->fqdn;
         }
         if (isset($fqdn)) {
-            $domains = str($fqdn)->explode(',')->map(fn (string $domain) => trim($domain))->filter();
-            $url = $domains->map(fn (string $domain) => Url::fromString($domain)->withPort(null)->__toString())->implode(',');
-            $fqdn = $domains->map(fn (string $domain) => Url::fromString($domain)->getHost())->implode(',');
-            if ((int) $this->application->compose_parsing_version >= 3) {
-                $this->coolify_variables .= 'COOLIFY_URL='.escapeShellValue($url).' ';
-                $this->coolify_variables .= 'COOLIFY_FQDN='.escapeShellValue($fqdn).' ';
-            } else {
-                $this->coolify_variables .= 'COOLIFY_URL='.escapeShellValue($fqdn).' ';
-                $this->coolify_variables .= 'COOLIFY_FQDN='.escapeShellValue($url).' ';
+            $domains = str($fqdn)->explode(',')
+                ->map(fn (string $domain) => trim($domain))
+                ->filter()
+                ->filter(fn (string $domain) => isValidDomainUrl($domain));
+            if ($domains->isNotEmpty()) {
+                $url = $domains->map(fn (string $domain) => Url::fromString($domain)->withPort(null)->__toString())->implode(',');
+                $fqdn = $domains->map(fn (string $domain) => Url::fromString($domain)->getHost())->implode(',');
+                if ((int) $this->application->compose_parsing_version >= 3) {
+                    $this->coolify_variables .= 'COOLIFY_URL='.escapeShellValue($url).' ';
+                    $this->coolify_variables .= 'COOLIFY_FQDN='.escapeShellValue($fqdn).' ';
+                } else {
+                    $this->coolify_variables .= 'COOLIFY_URL='.escapeShellValue($fqdn).' ';
+                    $this->coolify_variables .= 'COOLIFY_FQDN='.escapeShellValue($url).' ';
+                }
             }
         }
         if (isset($this->application->git_branch)) {
diff --git a/app/Support/DomainPortOverrides.php b/app/Support/DomainPortOverrides.php
index 320540ad6..853a6f339 100644
--- a/app/Support/DomainPortOverrides.php
+++ b/app/Support/DomainPortOverrides.php
@@ -34,6 +34,7 @@ public static function normalize(?string $fqdn, ?array $existing): array
         $normalizedDomains = collect(explode(',', $fqdn))
             ->map(fn (string $domain): string => trim($domain))
             ->filter()
+            ->filter(fn (string $domain): bool => isValidDomainUrl($domain))
             ->map(function (string $domain) use ($existingOverrides): array {
                 $portlessDomain = self::withoutPort($domain);
                 $parts = DomainUrlParts::split($domain);
diff --git a/tests/Unit/ApplicationDeploymentCoolifyUrlDomainsTest.php b/tests/Unit/ApplicationDeploymentCoolifyUrlDomainsTest.php
index f6684718e..8fb8e0bd6 100644
--- a/tests/Unit/ApplicationDeploymentCoolifyUrlDomainsTest.php
+++ b/tests/Unit/ApplicationDeploymentCoolifyUrlDomainsTest.php
@@ -44,6 +44,7 @@ function coolifyVariablesForFqdn(string $fqdn, string $composeParsingVersion = '
     // The created hook resets this, so it has to be set afterwards.
     $application->compose_parsing_version = $composeParsingVersion;
     $application->save();
+    Application::withoutGlobalScopes()->whereKey($application->id)->update(['fqdn' => $fqdn]);
 
     $job = new TestableCoolifyUrlDeploymentJob;
     $reflection = new ReflectionClass(ApplicationDeploymentJob::class);
@@ -92,3 +93,19 @@ function coolifyVariablesForFqdn(string $fqdn, string $composeParsingVersion = '
         ->toContain("COOLIFY_URL='https://a.example.com'")
         ->toContain("COOLIFY_FQDN='a.example.com'");
 });
+
+it('ignores a hostless stored domain while setting deployment variables', function () {
+    $variables = coolifyVariablesForFqdn('https://,https://a.example.com');
+
+    expect($variables)
+        ->toContain("COOLIFY_URL='https://a.example.com'")
+        ->toContain("COOLIFY_FQDN='a.example.com'");
+});
+
+it('does not set domain variables for a hostless stored fqdn', function () {
+    $variables = coolifyVariablesForFqdn('https://');
+
+    expect($variables)
+        ->not->toContain('COOLIFY_URL=')
+        ->not->toContain('COOLIFY_FQDN=');
+});
diff --git a/tests/Unit/DomainPortOverridesTest.php b/tests/Unit/DomainPortOverridesTest.php
index 42345e5df..9753b2d1f 100644
--- a/tests/Unit/DomainPortOverridesTest.php
+++ b/tests/Unit/DomainPortOverridesTest.php
@@ -34,3 +34,25 @@
     'www redirect' => ['https://example.com', 'https://www.example.com'],
     'non-www redirect' => ['https://www.example.com', 'https://example.com'],
 ]);
+
+it('drops hostless domains and their port overrides', function () {
+    $result = DomainPortOverrides::normalize(
+        'https://,https://example.com',
+        [
+            'https://' => 3000,
+            'https://example.com' => 8080,
+        ],
+    );
+
+    expect($result)->toBe([
+        'fqdn' => 'https://example.com',
+        'overrides' => ['https://example.com' => 8080],
+    ]);
+});
+
+it('clears an fqdn that contains only a hostless domain', function () {
+    expect(DomainPortOverrides::normalize('https://', ['https://' => 3000]))->toBe([
+        'fqdn' => null,
+        'overrides' => null,
+    ]);
+});