diff --git a/UPGRADE-8.0.md b/UPGRADE-8.0.md
index 40b4769883bad..c56e501e642fc 100644
--- a/UPGRADE-8.0.md
+++ b/UPGRADE-8.0.md
@@ -285,6 +285,11 @@ PropertyInfo
    }
    ```
 
+Routing
+-------
+
+ * Providing a non-array `_query` parameter to `UrlGenerator` causes an `InvalidParameterException`
+
 Security
 --------
 
diff --git a/src/Symfony/Component/Routing/CHANGELOG.md b/src/Symfony/Component/Routing/CHANGELOG.md
index 4ef96d53232fe..1c9b745370b22 100644
--- a/src/Symfony/Component/Routing/CHANGELOG.md
+++ b/src/Symfony/Component/Routing/CHANGELOG.md
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+8.0
+---
+
+ * Providing a non-array `_query` parameter to `UrlGenerator` causes an `InvalidParameterException`
+
 7.4
 ---
 
diff --git a/src/Symfony/Component/Routing/Generator/UrlGenerator.php b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
index d82b91898194a..32d57e9c8dd5d 100644
--- a/src/Symfony/Component/Routing/Generator/UrlGenerator.php
+++ b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
@@ -149,8 +149,7 @@ protected function doGenerate(array $variables, array $defaults, array $requirem
                 $queryParameters = $parameters['_query'];
                 unset($parameters['_query']);
             } else {
-                trigger_deprecation('symfony/routing', '7.4', 'Parameter "_query" is reserved for passing an array of query parameters. Passing a scalar value is deprecated and will throw an exception in Symfony 8.0.');
-                // throw new InvalidParameterException('Parameter "_query" must be an array of query parameters.');
+                throw new InvalidParameterException('Parameter "_query" must be an array of query parameters.');
             }
         }
 
diff --git a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
index 75196bd214aa2..72eb1af71d4af 100644
--- a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
+++ b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
@@ -1109,23 +1109,16 @@ public function testQueryParameterCannotSubstituteRouteParameter()
         ]);
     }
 
-    /**
-     * @group legacy
-     */
     public function testQueryParametersWithScalarValue()
     {
         $routes = $this->getRoutes('user', new Route('/user/{id}'));
 
-        $this->expectUserDeprecationMessage(
-            'Since symfony/routing 7.4: Parameter "_query" is reserved for passing an array of query parameters. ' .
-            'Passing a scalar value is deprecated and will throw an exception in Symfony 8.0.',
-        );
+        $this->expectException(InvalidParameterException::class);
 
-        $url = $this->getGenerator($routes)->generate('user', [
+        $this->getGenerator($routes)->generate('user', [
             'id' => '123',
             '_query' => 'foo',
         ]);
-        $this->assertSame('/app.php/user/123?_query=foo', $url);
     }
 
     protected function getGenerator(RouteCollection $routes, array $parameters = [], $logger = null, ?string $defaultLocale = null)