diff --git a/src/Mercure/Service/UrlService.php b/src/Mercure/Service/UrlService.php
index 70e424099..22f83f46f 100644
--- a/src/Mercure/Service/UrlService.php
+++ b/src/Mercure/Service/UrlService.php
@@ -32,7 +32,7 @@ public function __construct(
     public function getServerSideUrl(): string
     {
         if (empty($this->serverSideUrl)) {
-            return $this->getDefaultServerUrl();
+            throw new LogicException('Mercure server URL is not configured.');
         }
 
         return $this->serverSideUrl;
@@ -47,10 +47,6 @@ public function getClientSideUrl(): string
         return str_replace(Mercure::HOST_PLACEHOLDER->value, $this->getHostUrl(), $this->clientSideUrl);
     }
 
-    private function getDefaultServerUrl(): string
-    {
-        return $this->getHostUrl() . '/hub/.well-known/mercure';
-    }
 
     private function getDefaultClientUrl(): string
     {
diff --git a/tests/Unit/Mercure/Service/UrlServiceTest.php b/tests/Unit/Mercure/Service/UrlServiceTest.php
index 39031572a..aa564f515 100644
--- a/tests/Unit/Mercure/Service/UrlServiceTest.php
+++ b/tests/Unit/Mercure/Service/UrlServiceTest.php
@@ -28,15 +28,13 @@ public function testGetServerSideUrlWithCustomUrl(): void
         $this->assertSame('https://custom/mercure', $service->getServerSideUrl());
     }
 
-    public function testGetServerSideUrlWithDefault(): void
+    public function testGetServerSideUrlThrowsWhenNotConfigured(): void
     {
-        $service = new UrlService(
-            null,
-            null,
-            $this->createRequestStackWithRequest('https://example.com')
-        );
+        $service = new UrlService(null, null, new RequestStack());
 
-        $this->assertSame('https://example.com/hub/.well-known/mercure', $service->getServerSideUrl());
+        $this->expectException(LogicException::class);
+        $this->expectExceptionMessage('Mercure server URL is not configured.');
+        $service->getServerSideUrl();
     }
 
     public function testGetClientSideUrlWithCustomUrlReplacesPlaceholder(): void
@@ -66,10 +64,11 @@ public function testThrowsLogicExceptionWithoutRequest(): void
         $service = new UrlService(null, null, new RequestStack());
 
         $this->expectException(LogicException::class);
-        $service->getServerSideUrl();
+        $this->expectExceptionMessage('Mercure fallback URL resolution requires an active HTTP request.');
+        $service->getClientSideUrl();
     }
 
-    public function testDefaultUrlIncludesNonStandardPort(): void
+    public function testDefaultClientUrlIncludesNonStandardPort(): void
     {
         $service = new UrlService(
             null,
@@ -77,7 +76,7 @@ public function testDefaultUrlIncludesNonStandardPort(): void
             $this->createRequestStackWithRequest('http://localhost:8080')
         );
 
-        $this->assertSame('http://localhost:8080/hub/.well-known/mercure', $service->getServerSideUrl());
+        $this->assertSame('http://localhost:8080/hub', $service->getClientSideUrl());
     }
 
     private function createRequestStackWithRequest(string $uri): RequestStack