diff --git a/core/lib/Drupal/Core/Routing/CompiledRoute.php b/core/lib/Drupal/Core/Routing/CompiledRoute.php
index 775d4ae..ff76b11 100644
--- a/core/lib/Drupal/Core/Routing/CompiledRoute.php
+++ b/core/lib/Drupal/Core/Routing/CompiledRoute.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Core\Routing;
 
+use Drupal\Component\Utility\Unicode;
 use Symfony\Component\Routing\CompiledRoute as SymfonyCompiledRoute;
 
 /**
@@ -65,7 +66,10 @@ public function __construct($fit, $pattern_outline, $num_parts, $staticPrefix, $
     parent::__construct($staticPrefix, $regex, $tokens, $pathVariables, $hostRegex, $hostTokens, $hostVariables, $variables);
 
     $this->fit = $fit;
-    $this->patternOutline = $pattern_outline;
+    // Support case insensitive route matching by ensuring the pattern outline
+    // is lowercase.
+    // @see \Drupal\Core\Routing\RouteProvider::getRoutesByPath
+    $this->patternOutline = Unicode::strtolower($pattern_outline);
     $this->numParts = $num_parts;
   }
 
diff --git a/core/lib/Drupal/Core/Routing/RouteCompiler.php b/core/lib/Drupal/Core/Routing/RouteCompiler.php
index 52d0041..7185aa4 100644
--- a/core/lib/Drupal/Core/Routing/RouteCompiler.php
+++ b/core/lib/Drupal/Core/Routing/RouteCompiler.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\Core\Routing;
 
-use Drupal\Component\Utility\Unicode;
 use Symfony\Component\Routing\RouteCompilerInterface;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCompiler as SymfonyRouteCompiler;
@@ -38,8 +37,7 @@ public static function compile(Route $route) {
     // The Drupal-specific compiled information.
     $stripped_path = static::getPathWithoutDefaults($route);
     $fit = static::getFit($stripped_path);
-    // Store a lower-case pattern outline to enable case-insensitive matching.
-    $pattern_outline = Unicode::strtolower(static::getPatternOutline($stripped_path));
+    $pattern_outline = static::getPatternOutline($stripped_path);
     // We count the number of parts including any optional trailing parts. This
     // allows the RouteProvider to filter candidate routes more efficiently.
     $num_parts = count(explode('/', trim($route->getPath(), '/')));
@@ -56,22 +54,21 @@ public static function compile(Route $route) {
       // the matching in \Drupal\Core\Routing\RouteProvider::getRoutesByPath()
       // and by skipping it we more easily make the routing case insensitive.
       '',
-      // Set the regex to use UTF-8 and be case-insensitive.
-      $symfony_compiled->getRegex() . 'ui',
+      $symfony_compiled->getRegex(),
       $symfony_compiled->getTokens(),
       $symfony_compiled->getPathVariables(),
       $symfony_compiled->getHostRegex(),
       $symfony_compiled->getHostTokens(),
       $symfony_compiled->getHostVariables(),
       $symfony_compiled->getVariables()
-    );
+      );
   }
 
   /**
    * Returns the pattern outline.
    *
    * The pattern outline is the path pattern but normalized so that all
-   * placeholders are the string '%'.
+   * placeholders are equal strings and default values are removed.
    *
    * @param string $path
    *   The path for which we want the normalized outline.
diff --git a/core/lib/Drupal/Core/Routing/RouteProvider.php b/core/lib/Drupal/Core/Routing/RouteProvider.php
index 4586652..99f8d15 100644
--- a/core/lib/Drupal/Core/Routing/RouteProvider.php
+++ b/core/lib/Drupal/Core/Routing/RouteProvider.php
@@ -2,10 +2,10 @@
 
 namespace Drupal\Core\Routing;
 
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Cache\CacheTagsInvalidatorInterface;
-use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Path\CurrentPathStack;
 use Drupal\Core\PathProcessor\InboundPathProcessorInterface;
 use Drupal\Core\State\StateInterface;
@@ -332,6 +332,7 @@ protected function getRoutesByPath($path) {
     // or leading or trailing slashes. Convert to lower case here so we can
     // have a case insensitive match from the incoming path to the lower case
     // pattern outlines from \Drupal\Core\Routing\RouteCompiler::compile().
+    // @see \Drupal\Core\Routing\CompiledRoute::__construct()
     $parts = preg_split('@/+@', Unicode::strtolower($path), NULL, PREG_SPLIT_NO_EMPTY);
 
     $collection = new RouteCollection();
diff --git a/core/lib/Drupal/Core/Routing/Router.php b/core/lib/Drupal/Core/Routing/Router.php
index 80a31f7..861ccda 100644
--- a/core/lib/Drupal/Core/Routing/Router.php
+++ b/core/lib/Drupal/Core/Routing/Router.php
@@ -160,6 +160,104 @@ public function matchRequest(Request $request) {
   }
 
   /**
+   * Tries to match a URL with a set of routes.
+   *
+   * @param string $pathinfo
+   *   The path info to be parsed
+   * @param \Symfony\Component\Routing\RouteCollection $routes
+   *   The set of routes.
+   *
+   * @return array
+   *   An array of parameters
+   *
+   * @throws \Symfony\Component\Routing\Exception\ResourceNotFoundException
+   *   If the resource could not be found.
+   * @throws \Symfony\Component\Routing\Exception\MethodNotAllowedException
+   *   If the resource was found but the request method is not allowed.
+   */
+  protected function matchCollection($pathinfo, RouteCollection $routes) {
+    // Try a case sensitive match.
+    $match = $this->_matchCollection($pathinfo, $routes, TRUE);
+    // Try a case in-sensitive match.
+    if ($match === NULL) {
+      $match = $this->_matchCollection($pathinfo, $routes, FALSE);
+    }
+    return $match;
+  }
+
+  /**
+   * Tries to match a URL with a set of routes.
+   *
+   * This code is very similar to Symfony's UrlMatcher::matchCollection() but it
+   * supports case insensitive matching. Also the static prefix optimisation is
+   * removed as this duplicates work done by the query in
+   * RouteProvider::getRoutesByPath().
+   *
+   * @param string $pathinfo
+   *   The path info to be parsed
+   * @param \Symfony\Component\Routing\RouteCollection $routes
+   *   The set of routes.
+   * @param bool $case_sensitive
+   *   Determines if the match should be case sensitive of not.
+   *
+   * @return array|null
+   *   An array of parameters. NULL when there is no match.
+   *
+   * @throws \Symfony\Component\Routing\Exception\ResourceNotFoundException
+   *   If the resource could not be found.
+   * @throws \Symfony\Component\Routing\Exception\MethodNotAllowedException
+   *   If the resource was found but the request method is not allowed.
+   *
+   * @see \Symfony\Component\Routing\Matcher\UrlMatcher::matchCollection()
+   * @see \Drupal\Core\Routing\RouteProvider::getRoutesByPath()
+   */
+  protected function _matchCollection($pathinfo, RouteCollection $routes, $case_sensitive) {
+    foreach ($routes as $name => $route) {
+      $compiledRoute = $route->compile();
+
+      // Set the regex to use UTF-8.
+      $regex = $compiledRoute->getRegex() . 'u';
+      if (!$case_sensitive) {
+        $regex = $regex . 'i';
+      }
+      if (!preg_match($regex, $pathinfo, $matches)) {
+        continue;
+      }
+
+      $hostMatches = array();
+      if ($compiledRoute->getHostRegex() && !preg_match($compiledRoute->getHostRegex(), $this->context->getHost(), $hostMatches)) {
+        continue;
+      }
+
+      // check HTTP method requirement
+      if ($requiredMethods = $route->getMethods()) {
+        // HEAD and GET are equivalent as per RFC
+        if ('HEAD' === $method = $this->context->getMethod()) {
+          $method = 'GET';
+        }
+
+        if (!in_array($method, $requiredMethods)) {
+          $this->allow = array_merge($this->allow, $requiredMethods);
+
+          continue;
+        }
+      }
+
+      $status = $this->handleRouteRequirements($pathinfo, $name, $route);
+
+      if (self::ROUTE_MATCH === $status[0]) {
+        return $status[1];
+      }
+
+      if (self::REQUIREMENT_MISMATCH === $status[0]) {
+        continue;
+      }
+
+      return $this->getAttributes($route, $name, array_replace($matches, $hostMatches));
+    }
+  }
+
+  /**
    * Returns a collection of potential matching routes for a request.
    *
    * @param \Symfony\Component\HttpFoundation\Request $request
diff --git a/core/modules/system/src/Tests/Routing/RouterTest.php b/core/modules/system/src/Tests/Routing/RouterTest.php
index db8a8af9..400ee0f 100644
--- a/core/modules/system/src/Tests/Routing/RouterTest.php
+++ b/core/modules/system/src/Tests/Routing/RouterTest.php
@@ -113,13 +113,18 @@ public function testDuplicateRoutePaths() {
     $this->assertRaw('router_test.two_duplicate1');
 
     // Tests three routes with same the path. One of the routes the path has a
-    // different case. The route with the maximum fit and lowest sorting route
-    // name will match, regardless of the order the routes are declared.
+    // different case.
     $this->drupalGet('router-test/duplicate-path3');
     $this->assertResponse(200);
     $this->assertRaw('router_test.three_duplicate1');
+    // While case-insensitive matching works, exact matches are preferred.
     $this->drupalGet('router-test/Duplicate-PATH3');
     $this->assertResponse(200);
+    $this->assertRaw('router_test.three_duplicate3');
+    // Test that case-insensitive matching works, falling back to the first
+    // route defined.
+    $this->drupalGet('router-test/Duplicate-Path3');
+    $this->assertResponse(200);
     $this->assertRaw('router_test.three_duplicate1');
   }