diff --git a/src/applications/diffusion/controller/DiffusionCloneController.php b/src/applications/diffusion/controller/DiffusionCloneController.php
--- a/src/applications/diffusion/controller/DiffusionCloneController.php
+++ b/src/applications/diffusion/controller/DiffusionCloneController.php
@@ -6,6 +6,19 @@
     return true;
   }
 
+  /**
+   * Provide action label for a code repository URI
+   *
+   * @param PhabricatorRepository Repository
+   * @return PhutilSafeHTML Label of the Clone URI
+   */
+  private function getCloneLabel(PhabricatorRepository $repository) {
+    if ($repository->isSVN()) {
+      return phutil_tag_div('diffusion-clone-label', pht('Checkout'));
+    }
+    return phutil_tag_div('diffusion-clone-label', pht('Clone'));
+  }
+
   public function handleRequest(AphrontRequest $request) {
     $viewer = $request->getViewer();
     $response = $this->loadDiffusionContext();
@@ -23,24 +36,34 @@
     $warning = null;
 
     $uris = $repository->getURIs();
-    foreach ($uris as $uri) {
-      if ($uri->getIsDisabled()) {
-        continue;
-      }
 
-      if ($uri->getEffectiveDisplayType() == $display_never) {
-        continue;
+    // If Differential is uninstalled and the repo is observed (=not hosted),
+    // only expose its external canonical URI, ignoring all URIs' display
+    // preferences and ignoring if the observed canonical URI is enabled.
+    if (!id(new PhabricatorDifferentialApplication())->isInstalled() &&
+        !$repository->isHosted()) {
+      foreach ($uris as $uri) {
+        if ($uri->getEffectiveIOType() == PhabricatorRepositoryURI::IO_OBSERVE) {
+          $view->addProperty(
+            $this->getCloneLabel($repository),
+            $this->renderCloneURI($repository, $uri));
+          break;
+        }
       }
-
-      if ($repository->isSVN()) {
-        $label = phutil_tag_div('diffusion-clone-label', pht('Checkout'));
-      } else {
-        $label = phutil_tag_div('diffusion-clone-label', pht('Clone'));
+    } else {
+      foreach ($uris as $uri) {
+        if ($uri->getIsDisabled()) {
+          continue;
+        }
+
+        if ($uri->getEffectiveDisplayType() == $display_never) {
+          continue;
+        }
+
+        $view->addProperty(
+          $this->getCloneLabel($repository),
+          $this->renderCloneURI($repository, $uri));
       }
-
-      $view->addProperty(
-        $label,
-        $this->renderCloneURI($repository, $uri));
     }
 
     if (!$view->hasAnyProperties()) {