diff --git a/features/permalinks.feature b/features/permalinks.feature
index a69e059b..31c55105 100644
--- a/features/permalinks.feature
+++ b/features/permalinks.feature
@@ -142,3 +142,12 @@ Feature: Fancy permalinks
     And the _site directory should exist
     And I should see "I am PHP" in "_site/2016/i-am-php.php"
     And I should see "I am also PHP" in "_site/i-am-also-php.php"
+
+  Scenario: Use the same permalink twice
+    Given I have a "cool.md" page with permalink "/amazing.html" that contains "I am cool"
+    And I have an "awesome.md" page with permalink "/amazing.html" that contains "I am also awesome"
+    When I run jekyll build
+    Then I should get a zero exit status
+    And the _site directory should exist
+    And I should see "Conflict: The URL '" in the build output
+    And I should see "amazing.html' is the destination for the following pages: awesome.md, cool.md" in the build output
diff --git a/lib/jekyll/site.rb b/lib/jekyll/site.rb
index 76c1327f..1647f8ad 100644
--- a/lib/jekyll/site.rb
+++ b/lib/jekyll/site.rb
@@ -221,6 +221,7 @@ module Jekyll
     #
     # Returns nothing.
     def write
+      Jekyll::Commands::Doctor.conflicting_urls(self)
       each_site_file do |item|
         item.write(dest) if regenerator.regenerate?(item)
       end