diff --git a/src/__tests__/PhabricatorInfrastructureTestCase.php b/src/__tests__/PhabricatorInfrastructureTestCase.php
--- a/src/__tests__/PhabricatorInfrastructureTestCase.php
+++ b/src/__tests__/PhabricatorInfrastructureTestCase.php
@@ -12,10 +12,71 @@
    * This is more of an acceptance test case instead of a unit test. It verifies
    * that all symbols can be loaded correctly. It can catch problems like
    * missing methods in descendants of abstract base classes.
+   *
+   * We then perform some additional reflection-based checks.
    */
   public function testEverythingImplemented() {
-    id(new PhutilSymbolLoader())->selectAndLoadSymbols();
-    $this->assertTrue(true);
+    $symbols = id(new PhutilSymbolLoader())
+      ->selectAndLoadSymbols();
+
+    $classes = array();
+    foreach ($symbols as $symbol) {
+      if ($symbol['type'] == 'class') {
+        $classes[$symbol['name']] = new ReflectionClass($symbol['name']);
+      }
+    }
+
+    foreach ($classes as $class_name => $class) {
+      $parents = array();
+      $parent = $class;
+      while ($parent = $parent->getParentClass()) {
+        $parents[] = $parent;
+      }
+
+      $interfaces = $class->getInterfaces();
+
+      foreach ($class->getMethods() as $method) {
+        $visibility = $this->getVisibility($method);
+        $method_name = $method->getName();
+
+        foreach (array_merge($parents, $interfaces) as $extends) {
+          if ($extends->hasMethod($method_name)) {
+            $xmethod = $extends->getMethod($method_name);
+            $xvisibility = $this->getVisibility($xmethod);
+            if ($visibility != $xvisibility) {
+              $this->assertEqual(
+                $xvisibility,
+                $visibility,
+                pht(
+                  'Class "%s" implements method "%s" with the wrong '.
+                  'visibility. The method has visibility "%s", but it is '.
+                  'defined in parent "%s" with visibility "%s". In '.
+                  'Phabricator, a method which overrides another must '.
+                  'always have the same visibility.',
+                  $class_name,
+                  $method_name,
+                  $visibility,
+                  $extends->getName(),
+                  $xvisibility));
+            }
+
+            // We found a declaration somewhere, so stop looking.
+            break;
+          }
+        }
+      }
+    }
+
+  }
+
+  private function getVisibility(ReflectionMethod $method) {
+    if ($method->isPrivate()) {
+      return 'private';
+    } else if ($method->isProtected()) {
+      return 'protected';
+    } else {
+      return 'public';
+    }
   }
 
   /**