diff --git a/src/Symfony/Component/Routing/Generator/UrlGenerator.php b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
index 7adf2ed27e77c..dfecac9ee6862 100644
--- a/src/Symfony/Component/Routing/Generator/UrlGenerator.php
+++ b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
@@ -294,6 +294,17 @@ protected function doGenerate($variables, $defaults, $requirements, $tokens, $pa
             return $a == $b ? 0 : 1;
         });
 
+        // force string for an object. See https://bugs.php.net/bug.php?id=66966
+        foreach ($extra as $paramName => $param) {
+            if (!\is_object($param)) {
+                continue;
+            }
+            if (!\is_callable([$param, '__toString'])) {
+                throw new InvalidParameterException(sprintf('Error when generating an URL for "%s". Cannot convert object of type "%s" to string for parameter "%s".', $name, get_debug_type($param), $paramName));
+            }
+            $extra[$paramName] = (string) $param;
+        }
+
         // extract fragment
         $fragment = $defaults['_fragment'] ?? '';
 
diff --git a/src/Symfony/Component/Routing/Tests/Generator/StringableStub.php b/src/Symfony/Component/Routing/Tests/Generator/StringableStub.php
new file mode 100644
index 0000000000000..47ea8583b3c08
--- /dev/null
+++ b/src/Symfony/Component/Routing/Tests/Generator/StringableStub.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Symfony\Component\Routing\Tests\Generator;
+
+class StringableStub
+{
+    public function __toString()
+    {
+        return 'dummy';
+    }
+}
diff --git a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
index f006f4ce9d587..3acf908b5ee7c 100644
--- a/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
+++ b/src/Symfony/Component/Routing/Tests/Generator/UrlGeneratorTest.php
@@ -856,6 +856,23 @@ public function testFragmentsCanBeDefinedAsDefaults()
         $this->assertEquals('/app.php/testing#fragment', $url);
     }
 
+    public function testNonStringableObjectParameterCannotBeConvertedToString()
+    {
+        $object = new \stdClass();
+        $routes = $this->getRoutes('test', new Route('/testing'));
+        $this->expectException(InvalidParameterException::class);
+        $this->getGenerator($routes)->generate('test', ['param' => $object]);
+    }
+
+    public function testStringableObjectParameterIsConvertedToString()
+    {
+        $object = new StringableStub();
+        $routes = $this->getRoutes('test', new Route('/testing'));
+        $url = $this->getGenerator($routes)->generate('test', ['param' => $object]);
+
+        $this->assertEquals('/app.php/testing?param=dummy', $url);
+    }
+
     /**
      * @dataProvider provideLookAroundRequirementsInPath
      */