diff --git a/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php b/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php
--- a/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php
+++ b/src/applications/differential/field/DifferentialRevisionIDCommitMessageField.php
@@ -50,24 +50,10 @@
     $uri = new PhutilURI($uri_string);
     $path = $uri->getPath();
 
-    $matches = null;
-    if (preg_match('#^/D(\d+)$#', $path, $matches)) {
-      $id = (int)$matches[1];
-
-      $prod_uri = new PhutilURI(PhabricatorEnv::getProductionURI('/D'.$id));
-
-      // Make sure the URI is the same as our URI. Basically, we want to ignore
-      // commits from other Phabricator installs.
-      if ($uri->getDomain() == $prod_uri->getDomain()) {
-        return $id;
-      }
-
-      $allowed_uris = PhabricatorEnv::getAllowedURIs('/D'.$id);
-
-      foreach ($allowed_uris as $allowed_uri) {
-        if ($uri_string == $allowed_uri) {
-          return $id;
-        }
+    if (PhabricatorEnv::isSelfURI($uri_string)) {
+      $matches = null;
+      if (preg_match('#^/D(\d+)$#', $path, $matches)) {
+        return (int)$matches[1];
       }
     }
 
diff --git a/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php b/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php
--- a/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php
+++ b/src/applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php
@@ -13,6 +13,7 @@
       "D123\nSome-Custom-Field: The End" => 123,
       "{$base_uri}D123" => 123,
       "{$base_uri}D123\nSome-Custom-Field: The End" => 123,
+      'https://www.other.com/D123' => null,
     );
 
     $env = PhabricatorEnv::beginScopedEnv();
diff --git a/src/infrastructure/env/PhabricatorEnv.php b/src/infrastructure/env/PhabricatorEnv.php
--- a/src/infrastructure/env/PhabricatorEnv.php
+++ b/src/infrastructure/env/PhabricatorEnv.php
@@ -406,21 +406,44 @@
     return rtrim($production_domain, '/').$path;
   }
 
-  public static function getAllowedURIs($path) {
-    $uri = new PhutilURI($path);
-    if ($uri->getDomain()) {
-      return $path;
+
+  public static function isSelfURI($raw_uri) {
+    $uri = new PhutilURI($raw_uri);
+
+    $host = $uri->getDomain();
+    if (!strlen($host)) {
+      return false;
     }
 
+    $host = phutil_utf8_strtolower($host);
+
+    $self_map = self::getSelfURIMap();
+    return isset($self_map[$host]);
+  }
+
+  private static function getSelfURIMap() {
+    $self_uris = array();
+    $self_uris[] = self::getProductionURI('/');
+    $self_uris[] = self::getURI('/');
+
     $allowed_uris = self::getEnvConfig('phabricator.allowed-uris');
-    $return = array();
     foreach ($allowed_uris as $allowed_uri) {
-      $return[] = rtrim($allowed_uri, '/').$path;
+      $self_uris[] = $allowed_uri;
     }
 
-    return $return;
-  }
+    $self_map = array();
+    foreach ($self_uris as $self_uri) {
+      $host = id(new PhutilURI($self_uri))->getDomain();
+      if (!strlen($host)) {
+        continue;
+      }
+
+      $host = phutil_utf8_strtolower($host);
+      $self_map[$host] = $host;
+    }
 
+    return $self_map;
+  }
 
   /**
    * Get the fully-qualified production URI for a static resource path.
diff --git a/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php b/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php
--- a/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php
+++ b/src/infrastructure/env/__tests__/PhabricatorEnvTestCase.php
@@ -218,4 +218,39 @@
     $this->assertFalse($caught instanceof Exception);
   }
 
+  public function testSelfURI() {
+    $base_uri = 'https://allowed.example.com/';
+
+    $allowed_uris = array(
+      'https://old.example.com/',
+    );
+
+    $env = PhabricatorEnv::beginScopedEnv();
+    $env->overrideEnvConfig('phabricator.base-uri', $base_uri);
+    $env->overrideEnvConfig('phabricator.allowed-uris', $allowed_uris);
+
+    $map = array(
+      'https://allowed.example.com/' => true,
+      'https://allowed.example.com' => true,
+      'https://allowed.EXAMPLE.com' => true,
+      'http://allowed.example.com/' => true,
+      'https://allowed.example.com/path/to/resource.png' => true,
+
+      'https://old.example.com/' => true,
+      'https://old.example.com' => true,
+      'https://old.EXAMPLE.com' => true,
+      'http://old.example.com/' => true,
+      'https://old.example.com/path/to/resource.png' => true,
+
+      'https://other.example.com/' => false,
+    );
+
+    foreach ($map as $input => $expect) {
+      $this->assertEqual(
+        $expect,
+        PhabricatorEnv::isSelfURI($input),
+        pht('Is self URI? %s', $input));
+    }
+  }
+
 }