diff --git a/src/Routing/Route.php b/src/Routing/Route.php
index f3eb05a0..e4532e8d 100644
--- a/src/Routing/Route.php
+++ b/src/Routing/Route.php
@@ -300,6 +300,12 @@ private function preprocessParams(array &$params): bool
 			$fixity = $meta[self::FIXITY] ?? null;
 
 			if (!isset($params[$name])) {
+				if ($fixity === self::CONSTANT) {
+					if ($meta[self::VALUE] === null) {
+						continue;
+					}
+					return false; // wrong parameter value
+				}
 				continue; // retains null values
 			}
 
diff --git a/tests/Route/fixedParameter.phpt b/tests/Route/fixedParameter.phpt
index c3fd4ed8..0d9b437d 100644
--- a/tests/Route/fixedParameter.phpt
+++ b/tests/Route/fixedParameter.phpt
@@ -21,10 +21,7 @@ testRouteIn($route, '/?const=foo', ['const' => 'hello', 'test' => 'testvalue'],
 
 testRouteIn($route, '/?const=hello', ['const' => 'hello', 'test' => 'testvalue'], '/?test=testvalue');
 
-Assert::same(
-	'http://example.com/',
-	testRouteOut($route, [])
-);
+Assert::null(testRouteOut($route, []));
 
 Assert::null(testRouteOut($route, ['const' => 'foo']));
 
@@ -33,7 +30,4 @@ Assert::same(
 	testRouteOut($route, ['const' => 'hello'])
 );
 
-Assert::same(
-	'http://example.com/',
-	testRouteOut($route, ['const' => null])
-);
+Assert::null(testRouteOut($route, ['const' => null]));
diff --git a/tests/Route/optional.autooptional3.phpt b/tests/Route/optional.autooptional3.phpt
index 03a04328..6a422cf3 100644
--- a/tests/Route/optional.autooptional3.phpt
+++ b/tests/Route/optional.autooptional3.phpt
@@ -13,9 +13,7 @@ use Tester\Assert;
 require __DIR__ . '/../bootstrap.php';
 
 
-$route = new Route('<presenter>/<default=123>/<required>', [
-	'action' => 'default',
-]);
+$route = new Route('<presenter>/<default=123>/<required>', []);
 
 testRouteIn($route, '/presenter/');
 testRouteIn($route, '/presenter/abc');
@@ -24,7 +22,6 @@ testRouteIn($route, '/presenter/abc/');
 testRouteIn($route, '/presenter/abc/xyy', [
 	'presenter' => 'presenter',
 	'default' => 'abc',
-	'action' => 'default',
 	'test' => 'testvalue',
 	'required' => 'xyy',
 ], '/presenter/abc/xyy?test=testvalue');